Fresh raspberries and mint leaves, for optional garnish
In a heavy saucepan, cook thawed raspberries and Splenda until the raspberries soften, about 5 minutes. Press the raspberries through a wire-mesh strainer into a liquid measuring cup; discard the solids and seeds. Let the strained juice cool completely.
While the raspberry juice cools, measure an equal volume of cream into a mixing bowl. (For example, if the berries yield 2/3 cup juice, use 2/3 cup cream.) Whip cream until stiff peaks form.
With a spatula, gently fold raspberry juice into the whipped cream. Cover and refrigerate until cold.
To serve, spoon the espuma into serving glasses or bowls. If desired, top with a few fresh raspberries and mint leaves.