My Pastry instructor told us in class that you could substitue any liquid for the liquid listed in a recipe unless that liquid is buttermilk. So if a recipe calls for milk, you could replace it with fruit juice, coffee, fruit puree etc. But in my head, I keep thinking that if you take milk out of a recipe and replace it with something like juice, you are altering the fat in the recipe and this wouldn't work well.
Does anyone have an opinion on that? I would like to replace the milk in this recipe with peach puree:
Confetti Cakes (Elisa Strauss)
YIELD: three 9 inch rounds (I do 2 if I'm using 3 inch high pans), one half sheet (13x18 inches), 24 cupcakes

INGREDIENTS

2 cups of cake flour
1 3/4 cup + 1 1/2 tsp of AP flour
2 1/4 tsp of baking powder
1 cup (2 sticks) of unsalted butter
3 cups of granulated sugar
3/4 tsp of salt
1 tbsp of vanilla extract
1 cup of egg whites or pasteurized eggs whites in liquid form
1 1/2 cup cups of milk

You are right.

Here'[s what I do with allergies and it works for me. Put some butter in the measuring cup cand then add the puree. Now the fat is replaced.

BUT...

That is not how I do subs. It doesn't mean mine is the only way, but this method works every time. No surprises.

Find a recipe that already has a puree and always use the same recipe for fruit puree recipes.

I have one that is one of my absolute favorite cakes. It's a strawberry cake, but blackberry, peach, or any puree will work. If you would like the recipe, just pm me. It's a real winner of a recipe. Susan