For the balsamic vinegar and agave nectar glaze: Put the balsamic vinegar and agave in a small saucepan over medium heat. Bring to a simmer and cook until the mixture comes together and thickens. Set aside to cool slightly. Rim a cocktail glass with the glaze.
For the tomato slice: Add the fresh tomato water and Basil-Infused Vodka to a cocktail shaker, add large ice cubes, shake vigorously and double-strain into the prepared glass. Add the foam on top, garnish with the basil leaf and serve.
Combine the vodka and basil leaves and let steep for at least 2 days. Strain out the basil before serving.
To make tomato water, line a mesh strainer with cheesecloth and place over a bowl. Puree 1 to 2 Roma tomatoes in a blender. Pour the liquid through the lined strainer and discard the solids.