In a large bowl, sift together flour, cornmeal, baking powder and salt. In a separate bowl, whisk together sour cream, oil, egg, sugar and baking soda. Gently fold wet ingredients into dry ones until just combined. Fold in corn, ricotta and thyme.
Melt butter in a 9 inch cast-iron skillet over medium high heat, tilting pan to coat bottom and sides completely. Cook butter 2 to 3 minutes, until it starts to color and smell nutty. Scrape batter into skillet; smooth surface with a rubber spatula.
Bake until bread is golden and a toothpick inserted in center comes out clean, 25 to 30 minutes. Let cool 5 minutes. Cut into wedges and serve.
Notes
If you don't have a 9-inch cast-iron skillet, you can substitute a 9 inch square (or round) pan for baking. If you use a separate pan, just brown the butter in a small pan and then transfer it to your desired pan for baking and scrape batter on top.