To make the Earl Grey Tea Syrup, combine 1/2 cup of sugar and 1/2 cup of water. Remove from heat and add Earl Grey tea bag and let stand 15 minutes. Remove tea bags and let syrup cool before pouring into an airtight container.
Shake 2 oz Amaro di Angostura, 3/4 oz Earl Grey Tea syrup and 1/2 oz lemon juice in an ice-filled shaker, then strain into an ice-filled highball glass. Top with 3 oz tonic water and gently stir; garnish with a lemon twist.