1. In a food processor, pulse together the flour, cornmeal, sugar, baking powder, 3/4 teaspoon of the black pepper and 1/2 teaspoon of the salt. Add the butter and pulse until the mixture forms coarse crumbs. Pour in the milk a little at a time and pulse until the dough just comes together. Pulse in 1/4 cup of the cheddar.
2. Place dough on a floured surface and form into a 1/2-inch-thick circle. Wrap the disk tightly in plastic wrap and refrigerate.
3. Preheat the oven to 375 degrees. In a 9-inch ovenproof skillet, combine the sugar and 2 tablespoons water. Cook over medium heat, swirling the pan gently (do not stir), 3 to 5 minutes or until sugar melts and turns amber. Add the vinegar and swirl. Add the tomatoes, thyme and remaining salt and black pepper to the pan; toss gently to coat tomatoes with the caramel mixture. Cook until the juices have thickened slightly, about 5 minutes. Remove from heat.
4. Cut biscuit dough into 8 equal-size wedges and arrange them in a circle on top of tomato mixture. Sprinkle biscuits with remaining cheddar.
5. Transfer the cobbler to oven and bake until biscuits are golden, about 40 minutes.