Monday, July 7, 2014

Pastry Cream

Pastry Cream is the mirepoix of desserts.  Just like the sweated mixture of carrots, celery, and onions is more functional than delicious in and of itself, so is pastry cream.  Pastry cream might not taste like much, unless you think vanilla pudding is exciting, but it's one step away from becoming a fabulous filling with the addition of chocolate, praline, whipped cream, or butter.  I have a soft spot for diplomat cream: pastry cream with folded in whipped cream.  Add a little ganache to that and it's a wicked chocolate mousse.  The possibilities are endless and can be whipped up in minutes once you get your pastry cream right.

Last week, I made batch after batch of pastry cream until I got the answer to the persistent pastry cream questions that were bothering me for years.

Flour or Cornstarch?
Cornstarch!  The pastry cream made with all flour had a starchy taste after chilling even though I cooked it for 8 minutes to help get rid of that unpleasant taste.  The only downside to cornstarch is that you can't freeze the cream, but pastry cream takes 10 minutes and can be made 2 days ahead, so I don't see a reason to freeze it unless you run a wholesale pastry business.  A mixture of cornstarch and cake flour works well too, but not everyone has cake flour on hand.

Is it ok to cut down on sugar?
Messing with amounts of ingredients is a recipe for disaster when it comes to pastry, but in this case the amount of sugar is flexible.  I cut it down a bit and nothing terrible happened.  You can even skip it completely if folding in a very sweet flavoring, like dulce de leche.  

Why does my pastry cream thin out after sitting in the fridge?
This is a classic beginner mistake.  Intuitively, overcooking a custard seems wrong, so I always waited just until my cream thickened and took it off the heat.  Turned out that was a big mistake.  Amylase enzyme present in eggs gradually breaks down the starch and thins out the pastry cream.  But this enzyme can be destroyed if the pastry cream is allowed to simmer for a few minutes.  How can you let a custard simmer without curdling it?  That's where the starch comes in.  It interferes with cross-linking of egg proteins and doesn't allow them to coagulate.  How lucky is that?

Vanilla Bean or Extract?
I know some people obsess over the little specs of real vanilla, but I don't feel that it's a deal breaker to use vanilla extract in pastry cream if it is one of many components of a dessert.  When I was doing my tests, I certainly wasn't going to sacrifice $50 worth of vanilla beans, so I used extract.  When I finally got a perfect batch of diplomat cream (pastry cream with whipped cream), I filled some eclair shells with it, dunked them into ganache and my husband proclaimed them the best eclairs even without the real vanilla bean.  I suggest you don't waste real vanilla beans on your first try, but once you get the hang of pastry cream, go for the bean.

Do you need to strain the pastry cream?
Most recipes instruct you to strain the custard before heating it up.  The reason for that is the presence of chalazae in the egg yolks.  They are white cordlike strands of egg white protein attached to the yolk that can't completely dissolve.  Straining is always the safest way to go, but unless you are making a huge batch, you can easily fish them out with a little fine mesh skimmer before cooking the sauce. 

Egg Yolks or Whole Eggs?
I've tried pastry creams with all yolks, all whole eggs, and a mixture of the two.  All yolks didn't make it much tastier, but required more work to separate all those yolks.

How careful do I need to be when tempering the eggs?
Most pastry cream recipes starts by scaring you into thinking that the eggs can scramble if you look at the them crooked.  And most recommend to pour the hot dairy in slowly.  The conscientious person that I am, I drizzled all of my milk/cream mixture in a tiny little stream thinking better safe than sorry.  Turns out this was creating a problem.  The dairy cooled off so much during my drizzling that it took 10 minutes to return it back to a boil.  No matter how carefully I was to stir the cream, it would often start to ooze out fat and look like broken mayo.  The reality is that unless you dump the entire pot of boiling dairy into fridge cold eggs without stirring, they won't scramble -- the cornstarch won't let them.  You should warm the eggs up with a splash of hot diary, but from then on, proceed without fear.  Dump the eggs into the boiling dairy all at once and you'll be 1 minute away from nice thick cream.  

Pastry Cream
This is the most foolproof recipe for pastry cream that I found.
Adopted from Rose Levy Beranbaum's Pie and Pastry Bible.

2 large eggs (100 grams weighed without the shell)
4 Tbsp corn starch (32 grams)
242 g whole milk (1 cup)
242 g cream (1 cup)
1/2 cup sugar (100 grams)
1/2 Vanilla bean, split lengthwise (or 1 and 1/2 tsp vanilla extract added in the end)
Pinch of salt
3 Tbsp unsalted butter (42 grams), cut into 3 pieces
  1. Line a small baking sheet (roughly 13"x9") with plastic wrap.  Have a fine mesh strainer set over a bowl ready near the stove.
  2. Whisk the eggs and cornstarch in a small bowl until completely smooth. 
  3. Place the milk and cream in a heavy 2-quart saucepan. It's best to either use a pan with rounded sides or get a French whisk (also known as Piano whisk) -- it's more narrow and gets into the corners of the pot better.
  4. Whisk ¼ cup or the milk/cream mixture into the egg mixture until smooth and the cornstarch is dissolved. 
  5. Add the sugar, vanilla bean if using, and salt to the saucepan with cream/milk. Bring the mixture to a full boil over medium heat, stirring occasionally. 
  6. Whisk 3 tbsp. of the hot milk/cream mixture into the egg mixture. Strain this mixture through a fine mesh strainer into a bowl. 
  7. Remove the vanilla bean and return the milk/cream to a boil over medium heat.
  8. Quickly add the egg mixture to the milk/cream mixture and whisk rapidly. The sauce should thicken. Bring to a boil while whisking. Once in a while pause for a couple of seconds to see if you got a boil. Then cook whisking vigorously for 30 seconds. 
  9. Remove from the heat. Whisk in vanilla extract if using instead of vanilla beans and the butter 1 piece at a time until completely incorporated.
  10. Immediately pour the pastry cream into a plastic lined baking sheet and lay a piece of plastic wrap on the surface to prevent a skin from forming. Allow the pastry cream to cool to room temperature, about 1 hour, then refrigerate overnight. 
  11. Before using, beat with a whisk to smooth out, but don't over-do this step as the cream can thin out.

My pastry cream is grainy
This doesn't happen with this recipe, since we are tempering the eggs.

My pastry cream is greasy and looks like broken hollandaise
This is usually due to the cream overcooking in places.  The usual culprits are: 1) the heat is too high 2) not enough sauce in the pan -- choose a pan that will result in a thick layer of cream 3) not bringing the sauce to the boil quickly enough -- once you tempered the eggs, don't be afraid to dump them into the boiling milk/cream mixture all at once

My pastry cream thins out after sitting in the fridge
You didn't cook it long enough.  After the bubbles start breaking the surface, it needs at least 30 seconds of cooking (a bit more is always safer).  Otherwise the eggs break down the starch.

My pastry cream is very stiff and not creamy after it sits in the fridge
This is perfectly normal.  Remember that it needs whipping before use.