1 cup (3¼ ounces) oat flour
1 cup (4 ounces) whole wheat flour, traditional or white whole wheat
1 teaspoon baking soda
½ teaspoon salt
½ cup (1 stick, 4 ounces) unsalted butter
⅔ cup (5 ounces) packed light or dark brown sugar
2 large eggs
1 cup (8 ounces) mashed banana (2 large or 3 medium bananas)
½ cup (4 ounces) plain yogurt, non-fat to full-fat
1 teaspoon vanilla extract
½ cup (1⅞ ounces) chopped pecans or walnuts
1 cup (6 ounces) chocolate or toffee chips (optional)
¾ cup (2⅝ ounces) old-fashioned rolled oats
⅓ cup (2½ ounces) packed light or dark brown sugar
½ teaspoon ground cinnamon
¼ teaspoon salt
2 tablespoons (1 ounce) unsalted butter, melted
¼ cup (1 ounce) chopped pecans or walnuts
Grease and flour an 8-inch-square pan. Preheat the oven to 350°F.
To make the cake batter:
Whisk together the flours, baking soda and salt in a medium bowl. Cream together the butter and sugar in a large mixing bowl until light and fluffy. Beat in the eggs, one at a time, stopping to scrape the sides and bottom of the bowl between additions. Mix in half the dry ingredients until moistened, then mix in the bananas, yogurt, and vanilla. Scrape down the sides and bottom of the bowl, then add the remaining dry ingredients and the nuts and chips, if using, mixing until evenly moistened. Transfer the batter to the prepared pan.
To make the topping:
Combine the oats, brown sugar, cinnamon and salt in a small mixing bowl until well blended. Stir in the melted butter until the moisture forms large crumbs; stir in the chopped nuts. Sprinkle the topping over the batter in the pan.
Bake until the edges pull away from the pan and a cake tester inserted in the center comes out clean, 40 to 45 minutes. Remove the cake from the oven and place on a rack to cool for 20 minutes before serving warm, with ice cream, or cool completely for later use.