We also tested this recipe using 1/2 cup melted butter in place of the canola oil and loved the rich, pound cake-like flavor it gave to these sweet cornbread muffins. They're delicious with peach preserves.
Preheat oven to 450°. Stir together cornmeal and sugar in a large bowl; make a well in center of mixture. Whisk together eggs, sour cream, and oil; add to cornmeal mixture, stirring just until dry ingredients are moistened. Fold in blackberries. Coat 2 muffin pans with vegetable cooking spray; spoon batter into muffin pans, filling three-fourths full.
Bake at 450° for 15 to 17 minutes or until tops are golden brown. Cool in pan on a wire rack 5 minutes. Remove from pan to wire rack.