Butter one large (9x5 and 3 inches high or 30x13 and 9 cm high) loaf pan. Preheat oven to 350°F (175°C).
In a medium-sized bowl, whisk or sift together the flours, baking soda, baking powder and salt. In a large mixing bowl, beat oil and sugar. Beat in the eggs. Beat in the banana. Add the flour mixture, buttermilk and vanilla and mix just until combined. Stir in ¾ of the chocolate chips, and nuts if desired.
Spread batter in prepared pan and sprinkle with remaining chocolate chips. Bake for about 50 minutes, until a toothpick inserted in the center of the bread comes out clean.
Cool in pan on wire rack for 10 minutes. Remove from pan and cool completely. Tip: to avoid smearing the chocolate chips on the top, lay the pan on its side and use a spatula pull the banana bread out of the pan. Place Banana Bread right side up on cooling rack.
Store tightly wrapped or in an airtight container for up to three days. Banana Bread can also be frozen for up to two months. Freezing in individually-wrapped slices is very practical.