Thanks to Evan Kleinman of KCRW Good Food. I am so making this...
Oil or butter for the baking dish
3 lbs ripe tomatoes (8 to 10 medium), cored and cut into wedges
1 Tablespoon cornstarch
Salt and freshly ground black pepper
1 cup all-purpose flour, plus more if needed
1 cup cornmeal
1 1/2 tsps baking powder
1/4 tsp baking soda
4 Tablespoons (1/2 stick) butter, cut into large pieces and refrigerated until very cold
1 egg, beaten
3/4 cup buttermilk, plus more if needed
1. Grease a square baking dish or a deep pie plate with the butter or oil. Preheat the oven to 375F.
2. Put the tomato wedges in a large bowl and sprinkle with the cornstarch and some salt and pepper. Toss gently to combine.
3. Put the flour, cornmeal, baking powder, and baking soda in a food processor along with a teaspoon of salt. Add the butter and pulse a few times until the mixture looks like coarse bread crumbs. Add the egg and buttermilk and pulse a few times more, until the mixture comes together in a ball. If the mixture doesn't come together, add a spoonful or two of flour. If the mixture is too dry, add a few drops of buttermilk.
4. Gently toss the tomato mixture again and spread it in the bottom of the prepared baking dish. Drop spoonfuls of the batter on top and smooth a bit with a knife. (Try to leave some gaps so that the steam from the tomato mixture will have a place to escape as the cobbler bakes.) Bake for 45 to 50 minutes, until golden on top and bubbly underneath. Cool to just barely warm or room temperature. To serve, scoop servings out with a large spoon.
From Mark Bittman.