Preheat oven to 350F.
Line two baking sheets with parchment paper and set aside.
Whisk eggs in a large bowl; add the sugar and whisk to combine.
Whisk in milk, butter, and vanilla until smooth.
In a separate bowl, whisk together flour, baking powder, and salt.
With an electric mixer on low, add flour mixture to the egg mixture one tablespoon at a time; continue to mix until thoroughly incorporated.
Remove mixing bowl from mixer and put in the fridge for 5 minutes.
Remove mixing bowl from fridge.
Lightly grease hands with cooking spray take a little dough and form into small balls; about 1-inch in size.
Place on prepared baking sheet and bake for 12 to 15 minutes, or until lightly browned on the bottom.
Remove from oven and let them rest on a cooling rack for a couple minutes, or until cool enough to handle.
Using a sharp knife, carefully cut out the bottoms of each cookie, making a nice well in the middle to fit the filling.
Reserve the cookie crumbs in a mixing bowl.