Chill tools: Place your mixing bowl and beaters in the freezer for ten minutes to help the cream whip effectively.
Whip topping: Add the chilled heavy cream, lemonade powder, and condensed milk to the cold bowl. Beat with a hand mixer on medium speed until stiff peaks form.
Prepare glasses: Fill two serving glasses with ice cubes and pour in the cold water or milk, leaving room at the top.
Assemble: Spoon the whipped lemonade topping generously over the iced base, garnish with a lemon slice, and serve immediately.
