Serve this cake straight from the pan.
Have all ingredients at room temperature, about 70°F. Preheat the oven to 375°F. Grease a 13 × 9-inch pan.
Whisk together in a large bowl until well blended:
Combine in a medium saucepan and bring to a boil, stirring constantly:
Pour the hot mixture over the dry ingredients and stir together just until smooth. Let cool for 5 minutes, then whisk in:
Scrape the batter into the pan and spread evenly. Bake until a toothpick inserted into the center comes out clean, 20 to 25 minutes.
Let cool completely in the pan on a rack.
If desired, spread with: