Chill your glass: Pop a tall glass into the freezer for 10 minutes. A cold glass keeps the shake thick and frosty.
Bloom the cocoa: In a small bowl, mix the cocoa powder with 1–2 tablespoons of the milk to form a smooth paste. This helps it blend without lumps and deepens the chocolate flavor.
Add to blender: Add the ice cream, remaining milk, cocoa paste, sugar, vanilla, and a pinch of salt to the blender.
If using espresso or syrup, add it now.
Blend briefly: Blend on low to medium just until smooth, 15–25 seconds. Stop and scrape the sides if needed. Overblending warms the shake and thins it out.
Taste and adjust: If it’s too intense, add a splash more milk.
Not sweet enough? Add another teaspoon of sugar or syrup. For a thicker shake, add another scoop of ice cream and pulse.
Serve immediately: Pour into the chilled glass.
Top with whipped cream and a sprinkle of cocoa or shaved chocolate if you like.