Step 1Place the raspberries and strawberries in a glass bowl and sprinkle with 4 to 6 tablespoons sugar (sweeter berries won't need as much sugar), the orange juice and the liqueur. Toss lightly. Cover and refrigerate for 20 minutes. Meanwhile, chill a bowl and beaters for whipping the cream. If you want to pipe the cream in rosettes, prepare a pastry bag fitted with a medium star tip.
Step 2Whip the cream with the remaining 1 teaspoon of sugar in the chilled bowl at medium-high speed until the cream thickens. Add the vanilla. For serving the cream in dollops, continue whipping until it is no longer runny and is just thick enough to hold its shape, somewhat like soft yogurt. For piping it in rosettes, whip the cream until it stands up in soft peaks when you lift the beaters.
Step 3To serve, spoon the berries into wine glasses or dessert dishes. Either spoon a dollop of whipped cream on each serving; or use a rubber spatula to fill the pastry bag, then pipe the whipped cream in decorative swirls or rosettes over the berries. Serve immediately.
Variation: To make Guilt-Free Berries Romanoff, for 1 or 2 portions of whipped milk, pour 1/2 cup nonfat milk into a chilled 3-cup jar (about 3 inches in diameter and 6 inches tall) or a tall glass; the milk will whip almost to the jar's top. Add 1 to 2 teaspoons of sugar or sweetener to taste and, if you like, 1/4 teaspoon vanilla powder. Using the whipping attachment of an immersion blender, whip the milk following the manufacturer's instructions, moving the whip slowly up and down. Spoon the whipped milk over the berries and serve immediately; whipped milk separates rapidly.