How much milk? Trying to make this now.

The recipe author says she based this on another recipe for a sweet brioche dough. That calls for 1/4 cup of milk to rehydrate the yeast, so that's what I believe would be used in this one. It's hard to give exact measurements for liquids in breadmaking, as how dry or damp your flour is, how big the eggs are, or even how much moisture is in the butter will have some effect. So you might start with the 1/4 cup, and have a little extra on hand if needed later in the mixing.