Dissolve the cornstarch in 50ml while milk, leave to rest.
In a small saucepan over medium high heat combine the heavy cream, the leftover milk, sugar, a pinch of salt and 2-3tbsp malted milk powder, stir, bring to an almost boil, add the cornstarch milk and cook constantly stirring until thickened. Take off heat, add the cream cheese, stir until smooth, cool to room temperature, then transfer into the fridge overnight.
Freeze in your ice cream maker according to the manufacturer's instructions adding the chopped Maltesers at the last couple of minutes of churning. Store in an airtight container or spoon right away.