In a small saucepan on medium-low heat add the milk and heavy cream. Whisk together it has become warm. Do not let it simmer or boil over.
In a small bowl, lightly whisk together the egg yolks, sugar, and cornstarch
Slowly add 1/2 of the warm milk into the egg yolk mixture whisking vigorously (this is going to temper the eggs).
Pour the egg yolk mixture back into the saucepan.
Whisk together constantly and continue to cook until it has become thick about 5 minutes. DO NOT IT BOIL!
Remove from heat and add in the butter and cake batter extract.
Pour into a heatproof bowl. Allow it to get to room temperature.
Place it in the freezer for two hours.
After the two hours pour the custard ice cream into a blender.
Add the milk and the ice.
Blend together until smooth.
Top with whipped cream and sprinkles.