Melt the butter and pour it into a 3 quart or 9x13x2 pan.
In a medium bowl combine the flour, 1 cup sugar, baking powder and salt. Pour in the half & half and mix until just combined. Pour the cake batter over top of the butter and set aside.
In a medium saucepan, add the strawberries, blackberries (NOT the raspberries), 1/2 cup of sugar and lemon juice. Heat on high, stirring gently and occasionally. Once the liquids come to a boil remove off of the heat, stir in vanilla and then spoon evenly onto the cake batter, the juices too!
Slid the baking dish onto the middle rack of your preheated oven and bake for 40 to 50 minutes (rotating halfway) until the top is richly golden and a cake tester comes out clean after inserted.
Allow the cake to cool for 15 to 20 minutes before dusting with powdered sugar. Serve spoonfuls into shallow dishes with a dollop of whipped cream or vanilla ice cream.