Corn Bread with Basil, Roasted Red Peppers and Monterey Jack Cheese

8 tablespoons (1 stick) chilled unsalted butter, cut into 1/2-inch pieces
1 cup chopped onion
1 3/4 cups yellow cornmeal
1 1/4 cups all purpose flour
1/4 cup sugar
1 tablespoon baking powder
1 1/2 teaspoons salt
1/2 teaspoon baking soda
1 1/2 cups buttermilk
3 large eggs
1 1/2 cups (lightly packed) grated Monterey Jack cheese (about 6 ounces)
1 1/3 cups corn kernels
1/2 cup chopped roasted red peppers
1/2 cup chopped fresh basil
 
   Preheat oven to 400°F. Butter 9x9x2-inch baking pan. Melt 1 tablespoon butter in medium nonstick skillet over medium-low heat. Add onion and sauté until tender, about 10 minutes. Cool.
   Mix cornmeal and next 5 ingredients in large bowl. Add 7 tablespoons butter and rub in with fingertips until mixture resembles coarse meal. Whisk buttermilk and eggs in medium bowl to blend. Add buttermilk mixture to dry ingredients and stir until blended. Mix in cheese, corn, red peppers, basil and onion. Transfer to prepared pan.
   Bake corn bread until golden and tester inserted into center comes out clean, about 45 minutes. Cool 20 minutes in pan on rack. (Can be prepared 8 hours ahead. Cool completely. Cover loosely with foil and let stand at room temperature. If desired, rewarm in 350°F oven about 10 minutes.)
   Cut corn bread into squares.