Bring 2 1/2 cups water, 1/2 cup each toasted pecans and maple syrup, 1/4 cup brown sugar, 1 teaspoon each vanilla and lemon juice, and a pinch of salt to a boil, then simmer, reducing to 3/4 cup, about 40 minutes. Strain and let cool. Stir about 3 tablespoons syrup into a glass and add about 8 ounces of seltzer, stirring until combined. Garnish with the pecans.
Photograph by Sam Kaplan