Prepare brownie mix with water, oil, and 3 eggs as directed by box.
Scoop the batter into the ice cream cones, about 3 tablespoons, or until it reaches the bottom of the wide ridge. You want them ⅔rds of the way full.
Place your ice cream cones in the baking dish of choice.
Bake in the preheated oven for 25-30 minutes or until a toothpick comes out clean. For a gooey center, 25 minutes should be good, no toothpick test needed. The top of the brownies will sink as it cools.
Let cool and serve with a scoop of vanilla ice cream on top.
Notes
Fill the brownie ice cream cones about ⅔ full, using the bottom ridge of the cone where it widens as a measuring gauge.To keep the cones upright while baking, use methods like placing them in a muffin tin or covering a baking dish with heavy-duty foil and poking holes for the cones to stand in.For transporting unfrosted cones to gatherings, decorate them on-site and store in an airtight container.If the cones are frosted, use a baking dish covered in foil with holes for the cones or an upside-down disposable aluminum baking pan on a baking sheet with holes for transport.