Pre heat oven to 350. Spray two mini muffin tins with non-stick spray and set aside.
In a microwave safe bowl, combine butter and sugar. Microwave on high until butter has melted. Stir to combine. Stir in cocoa, salt, baking powder and vanilla. Whisk in the eggs one at a time until smooth. Stir in flour just until combined. Spoon brownie batter by tablespoon into each mini muffin tin cavity. Bake for 13-15 minutes or until tops are set. Allow brownies to sit in pan until they are cool enough to touch. Using the back of a melon baller, teaspoon or your thumb, make an indentation into each brownie. Prepare filling.
To prepare the filling: combine egg yolk, milk and brown sugar in a saucepan. Add butter in chunks and cook over medium heat stirring constantly until thick, about 10 minutes.
Stir in vanilla, salt, coconut, pecans. Carefully place a teaspoon full of the filing into the center of each brownie.