Banana Kahlua Walnut Cake

Makes 12 servings.

Vegetable spray, for cake pan
1 3/4 cups all-purpose flour
1 1/2 cups granulated sugar
1 teaspoon baking soda
1/2 teaspoon salt
3 very ripe bananas, mashed
2 eggs, lightly beaten
1/2 cup oil
1/4 cup buttermilk or sour milk
3 teaspoons vanilla extract, divided
1 cup chocolate chips, for chocolate leaf garnish
1 teaspoon Crisco shortening, for chocolate leaf garnish
About 10 unblemished camellia leaves (or other small firm
    leaves), washed and dried, for chocolate leaf garnish
About 3 1/2 tablespoons Kahl