Preheat oven to 350°F. Stir eggs with sugar and vanilla. Add melted butter.
Sift ground chocolate with flour, baking powder, and salt. Stir into egg mixture.
Spread half the batter into a greased 8" square pan. Place chocolate squares in a single layer on top of batter. Cover the squares layer with the remaining batter. Bake 20 to 30 minutes. Cut into 16 to 20 squares.