Rhubarb Snacking Cake

Heat the oven to 350 degrees F. Lightly oil or butter a 9-inch square baking pan. Melt the butter. In a medium bowl, combine 2 tablespoons of the melted butter with the oats and ¼ cup of brown sugar. Mix welland set aside.

In a large bowl, mix the flours, remaining brown sugar, soda and salt. In a separate bowl, whisk together the yogurt and egg; slowly add the remaining 4 tablespoons melted butter, while whisking the mixture. Pour the yogurt mixture over the dry ingredients and stir just to combine. Quickly stir in the rhubarb. Scrape the batter into the prepared pan. Sprinkle with the topping, then bake for 30 to 35 minutes. A toothpick inserted in the center of the cake should come out with no wet batter sticking to it. Cool the cake on a rack. Serve warm, or wrap tightly and refrigerate for up to a week.