Prep the berries: Rinse and gently pat dry 2 cups of raspberries.
Set aside a handful for garnish. If your berries are very tart, toss them with 1 teaspoon powdered sweetener and let them sit 5 minutes.
Whip the cream: In a cold bowl, beat 1 cup heavy cream with a pinch of salt until soft peaks form. Sprinkle in 1–2 tablespoons powdered sweetener and 1 teaspoon vanilla.
Beat to medium peaks—fluffy, not stiff.
Make the cream base: In another bowl, stir 1 cup full-fat Greek yogurt or mascarpone until smooth. Add 1–2 tablespoons powdered sweetener, the lemon zest, and a drop or two of almond extract if using. Taste and adjust sweetness.
Fold together: Gently fold the whipped cream into the yogurt/mascarpone in two additions.
Aim for a light, mousse-like texture. Do not overmix.
Optional raspberry mash: Lightly mash half the raspberries with a fork to release some juice. This creates a ripple that looks pretty in layers.
Layer the parfaits: Spoon a layer of cream mixture into the bottom of 4 small glasses.
Add a layer of raspberries (some whole, some mashed). Repeat with another layer of cream, then berries.
Add crunch: Sprinkle chopped toasted almonds or keto granola between layers or on top for texture.
Chill briefly: Refrigerate 20–30 minutes to set the layers and meld flavors. Garnish with reserved berries and a little extra lemon zest before serving.