Blend raspberries, sugar, lemon juice, vanilla until smooth

Strain through fine-mesh strainer, press to extract liquid, discard seeds

Should have about 1 cup smooth puree

Refrigerate 30 minutes to chill completely

Beat cold heavy cream on medium-high until starts to thicken

Add powdered sugar, beat to stiff peaks

Set aside in refrigerator

In clean, dry bowl, beat egg whites with salt (and cream of tartar) on medium until foamy

Gradually add sugar, 1 tbsp at a time, while beating

Increase to high, beat until stiff glossy peaks form

Remove chilled puree from fridge

Gently fold ⅔ of puree into whipped cream with rubber spatula

Add egg whites to raspberry-cream mixture in three additions

Fold gently after each, using lifting motion

Optional: drizzle remaining puree over mousse, gently swirl

Spoon or pipe into serving glasses

Smooth tops with spoon

Cover with plastic wrap

Refrigerate at least 4 hours or overnight

Just before serving, garnish with raspberries, mint, whipped cream

Serve chilled