Chill your tools. Place the mixing bowl and beaters in the fridge or freezer for 10–15 minutes. Cold equipment helps the cream whip faster and fluffier.
Bloom the gelatin. In a small bowl, sprinkle gelatin over the cold water.
Let it sit for 5 minutes until spongy.
Melt the gelatin. Microwave the bloomed gelatin for 5–10 seconds, just until melted and clear. Let it cool for 3–4 minutes. It should be liquid but not hot.
Start the whip. Add cold heavy cream, powdered sugar, vanilla, and salt to the chilled bowl.
Beat on medium speed until it’s thickened slightly and trails begin to form, about soft peaks.
Stabilize. With the mixer on low, slowly stream in the cooled, melted gelatin. Once added, increase to medium-high and whip to firm peaks. The frosting should be smooth, billowy, and stable.
Don’t overbeat.
Use or store. Frost cakes or cupcakes right away, or transfer to a piping bag. If it firms up too much in the fridge, give it a brief whisk to refresh.