Preheat oven to 400˚F (200˚C). Grease 8 or 9-inch round layer pan. (Square will also work.)
Mix dry ingredients. In a medium bowl, stir together 1-1/3 cups Bisquick and 3 tablespoons sugar.
Mix wet ingredients. In another bowl, melt 2 teaspoons butter. Whisk in 1/2 cup cold milk and 1 large egg.
Combine and spread. Add wet to dry and stir just until combined. Pour into pan. (Don't worry if there doesn't seem to be enough batter. The topping adds a lot.)
Prepare topping. In a small bowl, mix 1/3 cup brown sugar, 1/3 cup Bisquick, and 1 teaspoon cinnamon. Cut in 1/4 cup softened butter until crumbly.
Add topping and bake. Sprinkle evenly over the batter. Bake for 13–14 minutes (9-inch pan) or 20–21 minutes (8-inch pan), until golden and a toothpick comes out clean.
Notes
Advanced PrepMay be mixed the night before, covered and refrigerated before baking in the morning. Add a few extra minutes to baking time.Two Ways to Add the ToppingIf you love gooey pockets of cinnamon-sugar (like in the first photo), make the topping Derinda’s way: melt the butter and stir it into the sugar and Bisquick before dropping it over the batter in clumps.Prefer a crumbly, evenly distributed topping? That’s how her mom, Kay, did it. Cut cold butter into the topping mixture with a fork or rub it in with your fingers, then sprinkle it over the top.