When making this drink, I recommend Cazadores Reposado Tequila. The woody and citrus notes of the tequila blend perfectly with the Aperol and grapefruit.
1 oz Cazadores Reposado Tequila
1 oz Aperol
1 oz Noilly Prat Extra Dry Vermouth
Stir all ingredients with ice and strain into a chilled glass. Top with crushed ice and garnish with a large slice of grapefruit.