How can I make pastry cream for a cake filling more a bit more firm/sturdy? How can I make a pastry cream for a cake filling a bit more sturdy/firm.  My recipe called for 5 egg yolks and 3 T. cornstarch, 1 1/2c. whole milk, 1/2c. whipping cream.
The egg yolks and cornstarch both serve as thickeners. Increasing the cornstarch is probably the most practical way to make that recipe firmer; try 5 tbsp as a start. (You could instead increase the amount of egg yolk; this will give you a more solid texture, rather than just a thicker one.)