Place a metal or glass mixing bowl and beaters in the freezer for 10-15 minutes to chill.
In a microwave-safe bowl, combine white chocolate chips with 1/2 cup heavy cream. Microwave at 50% power for 2 minutes, stirring halfway through, until smooth. Let cool to room temperature.
Pour remaining 1 1/2 cups cold heavy cream into chilled bowl. Whip on high speed for 3-5 minutes until stiff peaks form.
Add vanilla extract and optional powdered sugar to whipped cream. Fold in cooled white chocolate mixture gently with a spatula until fully combined with no streaks.
Spoon or pipe mousse into serving glasses. Cover and refrigerate for at least 3 hours or overnight for best results.
Before serving, garnish with fresh berries, white chocolate shavings, and mint leaves if desired.