Add 1 oz of juice from a Lemon (1), 1 oz of juice from a Grapefruit (1), Egg (1), Whiskey (1.5 fluid ounce), and Maple Syrup (0.5 ounce) to your shaker and dry shake (no ice!) for 60 seconds.
Add ice and shake for another 30 seconds.
Double strain into your chilled coupe glass.
Twist your grapefruit to release some oils, then drop it in. Top off with a few drops of your Angostura Bitters (to taste) and enjoy!