In a medium pot bring 4 cups water to a boil ( for the polenta).
Cut leeks (white and light green parts only) into ⅛ inch thin disks. You should have at least one cup or more. Heat butter in large skillet over medium high heat. Add leeks and pancetta, and stir for 2-3 minutes. Turn heat to medium and continue sauting until leeks become tender and pancetta begins to crisp, about 12 minutes. In the mean time, prep the corn and sage and add it to the mixture.
When the polenta water boils, turn heat to low, and whisk in 1 cup cornmeal ( polenta) until smooth. Add 1 ½ teaspoon salt, 1 teaspoon granulated garlic, and a few cracks pepper. Cover, and let cook on low 15-20 minutes. ( You will add butter and sour cream, at the end.)
In a heavy bottom skillet, heat 1 Tablespoon oil, over medium high. Pat fish dry on all sides and sprinkle with salt and pepper. When oil is hot, add fish, turn heat to medium and cook about 4 minutes, or until perfectly golden. Turn over and cook until done to your liking. Depending on how thick your fish is, cooking times will vary.
Right be fore serving the polenta, whisk in 1 tablespoon butter and ⅛ C plus 1 Tablespoon sour cream.
Divide polenta among 4 bowls. Top with seared fish. Spoon corn leek mixture over and around fish.