Cooked pudding mix
Closest match1 box (3.4 oz) instant pudding = 1 box cook-and-serve pudding mix, prepared and fully chilledThe same starch-and-sugar formula without the pre-gelatinisation, so it thickens by ordinary starch gelatinisation when heated instead of setting cold.
MethodCook it with the milk as directed and chill it completely before using it in a recipe that expected an instant set.
Trade-offTakes 20 minutes plus chilling rather than five minutes of whisking, and it will not set at all if stirred into a cold batter unheated.
Allergen checkBoth instant and cooked mixes are made to be prepared with milk and frequently contain milk derivatives in the powder itself, along with wheat starch or gluten-containing anti-caking agents in some brands. Neither is reliably dairy-free or gluten-free — read the box.