Pour vodka, lemon juice, and mint simple syrup into a cocktail shaker filled with ice and shake.
Strain into a glass filled with ice and top up the glass with club soda.
Garnish with a slice of lemon.
Notes
* To make mint simple syrup, combine equal parts sugar and water (I used 1/2 cup of each) in medium sized saucepan. Had a handful of fresh mint leaves. Gently heat over low heat and swirl until sugar has completely dissolved. Allow mixture to fully cool before using. Store in airtight container in refrigerator for up to several weeks.