In a small saucepan, stir together milk and sugar until combined.
Simmer over low heat for 20-30 minutes until the milk has thickened.
From Powdered Milk
Mix the sugar into hot water first while it is nice and warm but not boiling. This will allow the water to dissolve the sugar.
Once the sugar has dissolved you can add in the powdered milk and stir until smooth and creamy. This can be used as a substitution for condensed milk in a 1:1 ratio.
Notes
This recipe yields 8 ounces (1 cup) of condensed milk. The recipe can be doubled for a larger batch, but you may need to simmer the mixture a few minutes longer.