Wash the lemon thoroughly. Trim off both ends, cut it into quarters, and remove the white center and any seeds.

Add the lemon quarters and cold water to a blender. Pulse 3 times, being careful not to overblend, as the peel can become bitter.

Strain the mixture through a fine-mesh sieve, pressing gently to extract as much juice as possible. Return the strained juice to the blender.

Add the sweetened condensed milk and 150 g (about 1¼ cups) of ice cubes. Blend until smooth, creamy, and frothy.

Fill two glasses with extra ice, pour in the Brazilian Lemonade, garnish with lemon slices if desired, and serve immediately.