To make the lavender syrup, add the sugar and water to a small saucepan. Turn to medium-high heat and stir as the syrup warms and the sugar dissolves in the water, about 2 minutes. Continue to cook and bring to a strong simmer. Simmer for 3 minutes and remove the pan from the heat.

Stir in the lavender, let cool to room temperature, and then transfer the syrup with the lavender to a jar with a lid. Cover with the lid and infuse at room temperature for 24 hours. When ready to use, pour the syrup through a mesh strainer and discard the lavender. You will have enough syrup to make 6 to 8 cocktails.

To make the cocktail, add the chopped strawberry to an 8-ounce rocks glass. Add the lavender syrup and use a muddler to smash the berry and mix in the syrup. Pour in the vodka and stir.

Fill the glass with crushed ice. Top with sparkling mineral water. Stir, garnish with lavender, and serve.