1 Lit Torch + 1 Unlit Torch = 2 Lit Torches
(unfortunately cant use Lit Torch as a tool so it disappears from crafting grid, but you dont lose any lit torches in process)
(you can bulk craft, e.g. 10 Lit Torch + 10 Unlit Torch = 20 Lit Torches if you shift click)

Thx Lich {Lichen} for handholding me through mod creation process.