Preheat oven to 350°.
Spray one 9x5-inch loaf pan or four 6x3x2-inch loaf pans with vegetable spray.
In a small mixing bowl, whisk together buttermilk, egg, and olive oil.
In a large mixing bowl, whisk together flour, sugar, minced onion, baking powder, baking soda, salt, garlic powder, rosemary, and basil. Stir in Cheddar and Parmesan cheeses.
Add buttermilk mixture to flour mixture, and stir, blending well.
Pour into prepared pans.
Bake until a knife inserted near the center comes out clean, 45 to 65 minutes, depending on size of pan. Remove from pan, and let cool on a wire rack.
