Mix the lemon zest, sugar and 1/3 cup water in a small saucepan and bring to a boil. Cook for 3 minutes. Strain and let cool completely.
Into each of 2 chilled 10-ounce tumblers, add 1 1/2 shots sherry and 1 1/2 tablespoons lemon syrup. Fill the glass with chilled seltzer (tasting and stirring as you go to make sure the flavor is neither too sweet nor too dilute). Garnish and each with a lemon slice.
Before starting Food52 with Merrill, I was a food writer and editor at the New York Times. I've written several books, including "Cooking for Mr. Latte" and "The Essential New York Times Cookbook." I played myself in "Julie & Julia" -- hope you didn't blink, or you may have missed the scene! I live in Brooklyn with my husband, Tad, and twins, Walker and Addison.