Gather all ingredients and tools before starting.

If you don’t have simple syrup, make it by combining equal parts sugar and water and heating until the sugar dissolves. Let it cool.

Fill the cocktail shaker halfway with ice to chill the drink properly.

Using a jigger, measure and pour in 4 ounces of vodka, 2 ounces of fresh lemon juice, and 2 ounces of simple syrup into the shaker.

Secure the shaker lid and shake vigorously for about 15 seconds to aerate and chill the mixture.

Place a strainer on the shaker and strain the cocktail into a highball or rocks glass filled with fresh ice.

Garnish with a lemon slice on the rim or dropped into the glass.

Serve immediately and enjoy the refreshing vodka sour.