Hulled and quartered strawberries, 1/4 cup sugar, and vanilla extract are blended until completely smooth. Strain the puree through a fine-mesh sieve into a saucepan to remove seeds.

Heat the strained puree over medium-low heat, stirring, until the sugar is dissolved and the puree is warm (do not boil). Remove from heat.

In a small bowl, sprinkle the gelatin powder over cold water and let stand (bloom) for 5 minutes.

Gently melt the bloomed gelatin in a microwave or over a water bath, then pour and stir thoroughly into the warm strawberry puree. Let cool at room temperature for 15-20 minutes, until just slightly warm but still liquid.

In a large chilled bowl, whip 1.5 cups heavy cream to stiff peaks. In a separate bowl, whip the remaining 1/2 cup heavy cream to stiff peaks for topping.

Gently fold one-third of the main batch of whipped cream into the cooled strawberry base. Then fold the base back into the remaining two-thirds of whipped cream using a cut-and-fold motion until no white streaks remain.

Spoon or pipe the mousse into dessert cups, filling three-quarters of the way. Refrigerate for at least 2 hours, or until completely set.

Before serving, pipe or spoon a generous swirl of the reserved whipped cream on top of each cup. Garnish with a reserved strawberry slice and optionally mint.