This sweet, moist cake with its unusual brûléed topping is an excellent potluck companion. Make it a day or two before serving for best flavor.
Have all ingredients at room temperature, about 70°F. Preheat the oven to 350°F. Grease a 13 × 9-inch baking pan.
Combine in a medium bowl and let stand for 20 minutes:
Meanwhile, whisk together thoroughly in another medium bowl:
Beat in a medium bowl, or in a stand mixer with the paddle attachment, on high speed until light and fluffy, 4 to 6 minutes:
Beat in:
Beat in the oat mixture on low speed, then beat in the flour mixture. Scrape the batter into the pan and spread evenly. Bake until a toothpick inserted in the center comes out clean, about 30 minutes.
Let cool briefly in the pan on a rack. While still warm, ice with:
Broil as directed.