Mix the batter. Prepare the brownie batter using the water, oil, and eggs listed above. Do not follow the box instructions.
Fill the cones. Scoop about 3 tablespoons of batter into each cone, filling them about ⅔ full. Use the bottom ridge of the cone as a visual guide.
Set for baking. Place the filled cones upright in a baking dish, muffin tin, or prepared foil holder.
Bake. Bake for 25 to 30 minutes, or until a toothpick inserted comes out clean. Depending on cone size or fill level, additional baking time of up to 10 minutes may be needed.
Cool and serve. Let cones cool completely before serving. Top with ice cream or frosting if desired.
Notes
Filling level: Do not overfill. Cones should be about ⅔ full to prevent overflow.
Keeping cones upright: Use a muffin tin or a foil covered baking dish with holes poked through for stability.
Transporting: For unfrosted cones, store in an airtight container and decorate on site. For frosted cones, transport upright using a foil covered baking dish or an inverted disposable pan with holes.