1. Preheat oven to 350 degrees F. Lightly spray an 8- or 9-inch square pan with vegetable cooking spray.
2. In a small bowl, combine oats, walnuts, cinnamon, and brown sugar.
3. Place butter in a small saucepan over medium heat. When butter begins to melt, start stirring. Continue stirring as butter continues to melt and becomes foamy, being careful that butter doesn't burn. After about 3 to 4 minutes, butter will be a golden color with dark bits on the bottom of the pan. Remove from heat. Measure out 1 Tbsp. of the browned butter and add to oat mixture. Stir to combine until crumbly and set aside.
4. Pour remaining browned butter into a medium bowl, scraping in all the browned bits.
5. In a large bowl, combine flour, sugar, baking powder, baking soda, and salt. Whisk to combine. Make a well in the center.
6. To the bowl with the butter, whisk in egg, egg whites, sour cream, vanilla, almond extract if using, and buttermilk. Whisk until combined and pour over dry ingredients. Beat with electric mixer on medium speed just until smooth, or use a wooden spoon; batter will be thick. Pour batter into prepared pan and smooth surface. Sprinkle surface evenly with reserved topping.
7. Bake cake until lightly browned on edges and a sharp knife inserted in the center comes out clean (crumb topping may stick), about 28 to 30 minutes. Cool on a wire rack at least 15 minutes. Serve warm or at room temperature, cut into squares.
Source: Hannaford fresh Magazine, September - October 2014