Step 1

Bring 10 oz. ginger, peeled, coarsely chopped, 5 wide strips lemon zest, 1 cup fresh lemon juice (from 5–6 lemons), ¼ cup honey, pinch of cayenne pepper, pinch of kosher salt, and ½ cup water to a boil in a small saucepan. Reduce heat and simmer until mixture is darkened in color and reduced by about one third, 30–40 minutes.

Step 2

Strain tonic through a fine-mesh sieve into a small bowl or measuring glass, pressing on solids to release as much liquid as possible; discard solids (you should have ½–⅔ cup tonic).

Step 3

To serve hot, pour 2 Tbsp. tonic into each mug. Top with hot water as desired and garnish with lemon wheels or twists.

Step 4

To serve cold, pour 2 Tbsp. tonic into each ice-filled glass. Top with seltzer as desired and garnish with lemon wheels or twists.Do ahead: Tonic can be made 1 week ahead. Cover and chill.