Cut the watermelon into chunks and then blend the watermelon in a high-powered blender until it has a smooth consistency.
Pour the blended watermelon juice through a strainer to remove any pulp or seed chunks and then discard the leftover sediment.
Fill a copper mug or glass with ice and add the vodka, lime juice, mint leaves, and strained watermelon juice. Then add the ginger beer and give it a stir. Garnish with a mint sprig and lime wedge.
Use a seedless watermelon for this recipe so you'll have less to strain out of the juice.
You can triple the recipe ingredients to make enough for a full pitcher. Don't add ice to the pitcher because it will water it down. Store the pitcher in the fridge, put ice in your cup, and pour the watermelon moscow mule over the ice.
You could substitute other fruit (strawberries, blueberries, peaches) instead of watermelon if you prefer.
Make sure to strain the watermelon juice so you won't have chunks of pulp or seed sediment floating in your drink.
You could also put this mixture inpopsicle molds to make boozy frozen watermelon popsicles for a refreshing adult-only summer treat!
You could make this a watermelon moscow mule mocktail simply by omitting the vodka. The ginger beer is non-alcoholic.