Juice the lemons. Squeeze fresh lemons until you have 1 cup of juice. Strain out seeds if needed.
Mix the creamy base. Add lemon juice and sweetened condensed milk to a pitcher. Whisk until smooth and pale.
Add cold water. Slowly pour in the cold water while whisking.
Taste and adjust. Add more condensed milk for sweetness, more lemon juice for tartness, or more water if it tastes too strong.
Serve cold. Fill glasses with ice, pour the creamy lemonade over the top, and garnish with lemon slices or mint.
Notes
Use fresh lemon juice for the best flavor. Bottled lemon juice can taste flat or bitter.For frozen creamy lemonade, blend the lemon juice, condensed milk, water, and 3 cups of ice until slushy.Store covered in the refrigerator for up to 1 day without ice. Stir well before serving.