Preheat oven to 425°F (220°C). In large bowl, whisk together flour, 1 cup (250 mL) cornmeal, sugar, baking powder, baking soda and salt.
In separate bowl, whisk together eggs, buttermilk and 1/3 cup (75 mL) melted butter; stir into flour mixture just until moistened. Set aside.
Pour remaining butter into 9-in. (23-cm) cast-iron skillet set over medium heat on stovetop. Stir in brown sugar and maple syrup. When sugar melts and starts to bubble, stir in tomatoes and rosemary. Cook about 3 min., or until tomatoes start to soften (but remain whole). Sprinkle 2 tbsp (30 mL) cornmeal over tomatoes. Do not stir. Spoon reserved batter over top.
Transfer to oven. Bake 15 min., or until golden brown and cornbread springs back when gently pressed in centre. Transfer skillet to rack; cool 5 min. Unmold cake onto serving platter. Serve warm or at room temperature.
Serve with dollop of sour cream or Greek-style yogourt.
Substitute buttermilk with 1 cup (250 mL) milk soured with 1 tbsp (15 mL) lemon juice or vinegar. Let stand 15 min. before using.