1 box brownie mix, prepared according to package directions, cut into centimeter cubes
In a small saucepan, heat the butter on medium heat, swirling occasionally. The butter will melt and foam, just keep stirring. Eventually, small brown flecks will form at the bottom of the pan and the butter will smell toasted. Remove from heat and allow to cool slightly.
Mix the milk and cream in a medium saucepan. Scoop 3 tablespoons of milk into a small bowl and mix with cornstarch. Set aside.
Stir the sugar and corn syrup into the milk mixture and heat over medium heat until the sugar dissolves completely. Turn the heat to low and simmer for about 5 minutes. Be careful to not let the milk burn. Stir in the cornstarch mixture and simmer for an additional minute, then remove from heat and pour in brown butter.
Pour everything into an electric mixer and blend on high speed until completely emulsified (hold the lid tight with a towel!). Stir in vanilla extract and blend for 30 seconds more.
Pour the mixture into a freezer-safe container and freeze for at least 2 hours. Or, if chilling overnight, place in fridge.
When you’re ready to make your ice cream, cut half of your baked brownies into small cubes (you will not need the other half of the brownies). Set aside.
Churn in your ice cream maker according to instructions. Once fully churned, carefully fold in the brownie bits. Place in a freezer-safe container and allow to chill for at least two hours before serving!