1. In a medium bowl, whisk together flour, baking powder, rosemary (or basil), sugar, salt and pepper. Add cold butte. With your fingers or a pastry blender, rub butter nto dry ingredients until well incorporated and butter is the size of small peas. Toss in feta, stirring to incorporate. Create a small well in the center of the flour mixture. Add buttermilk and bring together all the ingredients with a fork. The dough will be rather shaggy. Dump dough onto a lightly floured work surface and lightly knead until it comes together. Wrap dough in plastic wrap and refrigerate until the filling is assembled.

2. To make the filling, preheat oven to 375 degrees F. Coat an 8x8 or 9x9-inch pan with nonstick spray (or a bit of butter) and set aside. Add 1 tablespoon olive oil to a medium skillet set over medium heat. Add onion and 1/4 teaspoon salt, Cook onion, stirring occasionally, until caramelized, about 15 minutes. Add garlic and cook for 1 minute, then remove from heat and pour into prepared dish. Set aside.

3. In a large bowl, toss together tomatoes, squash, remaining 1 1/2 tablespoons olive oil, flour, and thyme. Season with pepper and remaining 1/2 teaspoon salt. Distribute mixture evenly over onions, and bake filling for 25 minutes.

4. Meanwhile, remove biscuit dough from the fridge. On a lightly floured work surface, roll into a 3/4 or 1-inch thickness, cut into 6 biscuits with a round biscuit cutter. (Excess dough can be cut into rounds and frozen, then baked another time.) Remove partially cooked filling from oven and place biscuits on top. Brush biscuits with extra buttermilk and add a sprinkle or salt. Return pan to oven and bake for 15 to 20 minutes, until biscuits are golden brown and cooked through and tomato mixture is bubbling. Remove from oven and allow to cool for about 10 minutes before serving.