Preheat the oven to 350°F. Line a 9- by 13-inch baking pan with parchment paper.

For the brownies, sift together the flour, cocoa powder and baking powder into a bowl, then add the salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar until fluffy. Add the eggs and egg yolks. Cream on high speed until fully combined, light and fluffy.

Reduce the mixer speed to low and slowly add the dry ingredients. Mix until fully incorporated. Fold in the chocolate and frozen raspberries using a spatula.

Pour the batter into the lined pan and bake for 40 to 45 minutes, until a skewer inserted in the center comes out clean.

While the brownie batter is baking, make the icing. In the stand mixer fitted with the paddle attachment, combine the icing sugar, butter, cocoa powder, hot milk and vanilla. Beat until the mixture becomes soft and creamy.

As soon as the brownie mixture is cooked, spread the icing all over the top, while it is still warm (see note). Let cool completely, then cut into 24 squares.