In a very large mixing bowl, whip the heavy cream, cocoa powder, sugar, and vanilla in a large bowl at low speed until it begins to thicken, then on medium-high speed until it reaches medium peaks (peaks hold their shape, but the tips curl down). Spoon or pipe the whipped cream onto pies, cakes, ice cream, or fresh berries.
Notes
Use cold cream. It fluffs up faster and holds its shape better when cold.
Don’t overwhip, or it can turn grainy or start to separate. If you overwhip, gently stir in more cream until it's smooth again.
Sweeten to taste and use quality cocoa for the best flavor.
You don't need a whisk attachment on your mixer to make whipped cream. Regular beaters work fine.