Muddle the raspberries in the shaker with the sugar. Shake all ingredients except bitters without ice. Give it another shake with ice. Strain into a coupé. Garnish with a couple drops of bitters.
I think sweetness could be tweaked to taste. Maybe slightly more or less sugar.
Vanilla sugar: I split half a vanilla bean and put it in to 8 ounces of superfine sugar and let it sit for a week or so (honestly, I don't take the vanilla out).