Pan Dulce, (Conchas) Sweet Bread

Dough
1 tablespoon yeast
3/4 cup warm milk
1/2 cup sugar divided
1/2 cup melted butter
3 eggs
1 teaspoon salt
1 teaspoon vanilla
4 1/2 cups flour

Topping
1/2 cup soft butter
1 cup flour
1/2 cup powdered sugar
1 teaspoon vanilla