All you need to make homemade dulce de leche is 15 minutes! Take a large salad bowl, pour in the sweetened milk and cook on high for 3 minutes. Stir, then microwave again for 1 minute. Repeat the process 6 times, or until the mixture has cooked for at least 11 minutes. When the cooking time is up, pour in half a cup of milk and whisk. Pour the dulce de leche into a glass jar and refrigerate until cooled.