Cut the watermelon in pieces. Remove any seeds that could still be found in seedless varieties. (If you prefer a slushie version of the cocktail, freeze the pieces first).

Blend the watermelon in a blender or a pitcher using a handheld immersion blender. (If using frozen pieces add a splash of water to facilitate the blending process).

Optional: strain the watermelon juice.

Divide the chilled Kolsch style beer equally between three glasses. Wait for the foam to dissipate.

Gently add enough watermelon juice (or slush) into each glass to fill it almost ⅘ of capacity.

Shake the bourbon over ice and pour into each glass, dividing equally.

Stir the mixture inside each glass, garnish with fresh mint and small slice of watermelon or a mini watermelon skewer and serve.