Combine the lemon verbena leaves and ginger syrup in a cocktail shaker and muddle.
Add the remaining ingredients and ice and shake until well-chilled.
Strain into a double rocks glass filled with fresh ice.
Garnish with a Szechuan button.
*Yuzu-calamansi sour mix: Combine 1 cup water and 1 cup sugar in a saucepan. Heat slowly, stirring until sugar dissolves. Remove from heat and let cool. Combine with 1 cup freshly squeezed yuzu juice and 1 cup freshly squeezed calamansi juice.
**Ginger syrup: Combine 1 cup water, 1 cup sugar and ¼ pound ginger, peeled and thinly sliced, in a saucepan. Heat slowly, stirring until sugar dissolves. Simmer for 30 minutes. Remove from heat, let cool and strain out solids.