Pour the water into a small saucepan. Sprinkle the gelatin over the water, and let it sit for 2-3 minutes. Place the pan over medium low heat and stir until gelatin dissolves. Remove from heat and let cool completely.

Once the gelatin mixture has cooled, place 1 tablespoon of the whipping cream and the cream of tartar in a small ziplock bag. Seal the bag and shake it until cream of tartar has dissolved completely and there are no lumps. If there are lumps, use your fingers to work them out.

Pour the cream of tartar mixture into a large bowl (the bowl of your mixer if using a stand mixer) along with the rest of the whipping cream and the sugar.

Beat with a hand mixer or the whisk attachment on a stand mixer on medium speed for about 2 minutes. Once mixture begins to slightly thicken, slowly pour in the gelatin-water while continually mixing. Add the vanilla. Continue to mix until the cream is thick and smooth.

Be sure not to over-mix during the whisking process. Do not try for stiff peaks, you will just end up with a curdled mess. Once the cream is thick enough to spread, stop whisking. It will still look soft, but that is okay. Store in the fridge until used in your other recipe.