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.

The recipe begins by coating a 9-inch pie plate with butter and preheating the oven to 350 degrees F. Next, you whisk sugar, buttermilk, eggs, baking mix, melted butter, and vanilla together in a bowl ...