I add the strawberries, sugar, and lemon juice to a small saucepan and let them simmer over medium heat for about 5 to 7 minutes. I stir occasionally until the strawberries break down into a soft jam-like mixture.

I remove the pan from heat and blend the mixture until smooth. If I want it silky, I strain the puree through a fine mesh sieve to remove the seeds.

In a small bowl, I sprinkle the gelatin over cold water and let it sit for about 5 minutes until it becomes spongy.

I gently heat the gelatin for a few seconds in the microwave (or over low heat), just until it melts. Then I stir it into the warm strawberry puree and let it cool completely.

In a cold bowl, I whip the heavy cream with powdered sugar and vanilla until it holds soft peaks. I stop mixing when the cream becomes fluffy but not grainy.

Once the puree cools, I gently fold it into the whipped cream using a rubber spatula. I work slowly to keep the air in. The mousse turns a soft pink and smells incredible.

I refrigerate the mousse for at least 2 hours so it can set before spreading it between cake layers.