Shake firmly for ~10 seconds until well chilled, then strain into a chilled martini or wine glass.
Slowly top with Prosecco to preserve bubbles. Garnish with a lime slice or a few cranberries and serve.
Notes
Use a dry Prosecco to balance sweetness. Mix the base ahead and top with bubbles just before serving. Freeze a few cranberries and drop them in as ‘ice’ for a festive touch.