Preheat the oven to 350*F. Melt the butter in the bottom of a 9-inch square pan by placing it into the oven for two or three minutes. Sprinkle ½ cup of the sugar over the melted butter. Spoon the thawed and drained berries over top of the sugar. Set aside.

Cream all of the remaining ingredients together using an electric mixer on low speed to combine. Increase speed to medium and beat for a further 2 minutes, scraping down the bowl frequently. Pour the batter over the berries in the baking pan.

Bake in the oven for about 50 minutes, or until a toothpick inserted in the center of the cake comes out clean. Immediately place a large heatproof serving plate upside down onto the cake pan. Carefully flip the cake tin and plate over so that the tin is on top. Leave for several minutes so that the sauce can drizzle over the cake. Remove the tin and serve warm, cut into squares