Whisk milk, granulated sugar, vanilla extract or paste, and a pinch of salt in a mixing bowl until the sugar dissolves and the mixture is smooth.
2 cups milk
Chill the base briefly in a shallow dish at about 5°C until cold and glossy.
Freeze the base in the shallow dish for 15–20 minutes, until the edges start to set.
Scrape the edges with a spatula to gather the center and create a cohesive mass.
Crush ice in a freezer bag until coarse snow, or pulse briefly in a blender.
2 cups milk
Stir the crushed ice into the base until you get a loose, oozy slush.
2 cups milk
Zest lemon over the slush to brighten the aroma and lift the sweetness.
2 cups milk
Scoop into chilled glasses and serve with a straw, revealing pale, creamy slush with tiny ice crystals.