Place a coupe glass in the freezer to chill while you prepare the cocktail.
Fill a mixing glass (or the bottom half of a shaker) with 2 to 3 large ice cubes. Add the gin, sweet vermouth, blueberry liqueur, and lemon bitters to the mixing glass.
Stir rapidly with a bar spoon to mix and chill.
Use a Hawthorne strainer to strain the cocktail into the chilled coupe glass.
Spritz with a lemon peel by twisting it over the top of the glass, then garnish and serve.