Chill your coffee: Brew coffee in advance and let it cool completely in the fridge. Cold brew is naturally smoother and less acidic, but regular brewed coffee works well.
Mix the protein first: In a shaker bottle or blender, combine milk and protein powder.
Shake or blend until completely smooth. Do this before adding coffee to avoid clumps.
Sweeten and flavor: Add vanilla, sweetener, and any flavor boosts (cocoa, caramel, spices). Blend or shake again.
Combine with coffee: Fill a glass with ice. Pour in the coffee, then top with your protein-milk mixture.
Stir gently to swirl.
Taste and adjust: Add more milk for creaminess, more coffee for stronger flavor, or a pinch of salt to round out sweetness.
Optional blender method: For a frosty texture, blend everything with a handful of ice until slushy.