1Preheat oven to 350F.
2Melt the butter in a saucepan until there's no more foam. Set aside to cool slightly.
3In a bowl, mix the eggs, brown sugar and vanilla extract until the mixture is pale.
4In a separate bowl, mix the flour and baking powder together.
5Pour the melted butter into the egg/sugar mixture and stir to combine.
6Slowly stir the flour into the mixture.
7Knead with your hands to form a big ball of dough.
8Shape the cookies with your hands.
9Arrange them on a silicon mat or parchment paper lined baking sheet.
10Bake for 15 minutes.
11Meanwhile make the frosting filling. In a bowl, with an electric mixer, beat the softened butter and confectioner's sugar until the mixture is pale and smooth.
12With a pairing knife, scrape the seeds out of the vanilla bean, and add them to the frosting.
13Add water and mix to get a smooth mixture.
14When the cookies are cooled, spread a layer of frosting onto half of the cookies.
15Sandwich together with the remaining cookies.