Preheat oven to 375 F. Coat a skillet with or a 10-inch cake pan with butter, then dust with gluten-free flour.
If using thawed berries, gently toss with 2 teaspoons cornstarch. Arrange fruit on bottom of skillet.
Whisk together cream, milk, sweetener, eggs and vanilla in a mixing bowl until smooth.
In a separate bowl, combine gluten-free flour, baking powder and salt. Whisk the dry ingredients into the cream mixture until combined and no lumps remain. Alternatively, put both wet and dry ingredients in a high-speed blender and process until well combined.
Pour the mixture over the berries and cherries in the skillet. Place in the middle of the oven and bake for 35 minutes until golden and puffy.
Cool on a wire rack for a few minutes. The top will fall slightly and settle.. Dust with powdered sugar, if desired.
Serve warm with extra berries. If serving for breakfast, drizzle with maple syrup. If serving for dessert, consider whipped cream or ice cream.