2. Put butter and sugar into a medium mixing bowl and beat with an electric mixer on medium speed until light and fluffy, about 5 minutes. Add flour, baking powder, and salt and beat on medium speed until mixture resembles coarse crumbs, about 30 seconds. Add milk and continue beating, scraping sides and bottom of bowl with a rubber spatula as necessary, until batter is smooth, about 1 minute more (batter will be very thick). Using a soup spoon, drop batter by the heaping spoonful over berries in dish. Pour 1 cup boiling water over batter (water will smooth out the dollops of batter slightly).