Preheat the oven to 350°F. Lightly grease an 8 or 9 square pan, or 9 or 10 round pan.

Beat together the butter, sugar, baking powder, and salt until smooth.

Add the eggs, beating until thoroughly combined. The mixture may look somewhat coagulated; thats OK. Stir in the vanilla and optional flavor.

Add the flour, mixing to make a smooth, stiff batter.

Spread the batter in the pan. In the larger-sized pans, the batter will be spread fairly thin; thats OK.

Spread the berries on top. Sprinkle with the cinnamon-sugar.

Bake the cake for about 35 to 40 minutes, until a cake tester inserted into the center comes out clean, and the cake showing around the berries is a light golden brown. Remove it from the oven, and serve warm, or at room temperature.