To make brownies:
Preheat oven to 350 F, Grease a 13 x 9-inch pan; set aside.
Melt the margarine or butter in microwave; add cocoa powder and stir until smooth. Add sugar and eggs and beat well. In a separate bowl combine flour, Clabber Girl Baking Powder and salt. Add chocolate batter and beat well, about 2 minutes, until combined. Stir in chocolate chips.
Pour into prepared pan and bake at 350 F for 20 to 25 minutes. Cool in pan on wire rack. When brownies have cooled, cut into squares.
To make Ice Cream:
In a heavy bottomed medium saucepan, gradually whisk one cup of the milk into the Clabber Girl Corn Starch until the cornstarch is dissolved. Whisk in the remaining milk, cream and sugar. Cook over medium low heat, stirring constantly, until the mixture is simmering and slightly thickened, about 8 to 10 minutes.
Transfer to a medium bowl set in a larger bowl of iced water. Stir in the vanilla. Let sit, stirring frequently, until completely chilled.
Pour the mixture into the container of an ice cream maker and freeze according to the manufacturer's instructions. Transfer the frozen ice cream to a large, airtight container. Cover and freeze until firm and set, about 4 hours. Serve frozen.
Make individual sundaes by stacking a brownie, then ice cream then another brownie; top with ice cream and desired toppings.