Preheat the oven to 400. Line two baking sheets with parchment or silicone liners.
In a large bowl or the bowl of a stand mixer, beat together the butter and sugar until light and fluffy. Add the eggs and vanilla and beat until smooth. Add the flour, cocoa powder, baking powder, and salt, and mix until combined.
Roll the dough into golf ball sized balls and place 1 1/2 inches apart on the prepared baking sheets. Press down to flatten slightly. Bake for 9 - 10 minutes, or until the cookies look dry on top and are just slightly browned on the bottoms. Remove from the oven and let cool completely.
To make the frosting, puree half of the strawberries in a food processor or blender, until smooth. In a large bowl or the bowl of a stand mixer, beat the butter until light and fluffy. Add the powdered sugar, vanilla, and strawberry puree, and beat until smooth. Add additional powdered sugar as needed to make a spreadable frosting.
Spread the frosting on the cooled cookies, and top with a strawberry slice.