In a blender or food processor, combine the hulled strawberries, granulated sugar, and lemon juice. Blend until completely smooth and no chunks remain. Taste and adjust sugar if needed. Set aside.

In a large, clean, chilled bowl, pour the cold heavy cream. Add the powdered sugar and vanilla extract. Using a hand mixer or stand mixer with the whisk attachment, whip on medium-high speed until stiff peaks form. The cream should hold its shape when the whisk is lifted.

Gently pour about 3/4 of the strawberry puree into the whipped cream. Using a large spatula, fold the puree into the cream with gentle, sweeping motions from the bottom up until just combined and no white streaks remain. Be careful not to deflate the cream.

Divide the mousse evenly among 4 clear serving glasses or bowls. If using, drizzle the reserved puree on top and use a toothpick to create a swirl. Garnish each glass with a fresh strawberry half or slice. Serve immediately or chill for up to 1 hour for a slightly firmer texture.