Place ½ cup coarsely chopped fresh strawberries in the freezer while you prepare the other ingredients.
Beat 1 cup cold heavy cream, 1 tablespoon of the powdered sugar, and ½ teaspoon vanilla extract with the whisk attachment in a stand mixer on medium speed until stiff peaks form, 5 to 6 minutes. (Alternatively, whisk in a large bowl by hand.) Refrigerate while you prepare the fruit.
Pulse the chopped strawberries, 1 ½ cups frozen raspberries, and the remaining 2 tablespoons powdered sugar in a food processor until finely chopped and resembles a coarse meal, 15 to 20 (1-second) pulses.
Transfer to the bowl of whipped cream and gently fold together with a flexible spatula until just combined. Divide between 4 to 6 serving cups. Garnish with sliced strawberries if desired. Serve immediately.
