Proof is in the... filling. If you’ve ever picked up a box of Bisquick, you’ve likely seen one of its “impossibly easy” recipes printed on the box—dishes ranging from sweet pies to savory casseroles.

I’ve never met a pie I didn’t like, but custard-based pies are certainly my favorite. I love the creamy contrast of textures, their wonderful flavor and the fact that they’re often served cold. But ...