Golden Lentil Dip

In a medium pot over medium heat, combine the stock, lentils, onion, celery, saffron, salt, and pepper. Bring to a simmer and cook gently until the lentils are tender and light golden in color, 20 to 35 minutes, depending on the lentils. (If they begin to dry out, add water as needed.) Drain, reserving any remaining liquid. Transfer the lentil mixture to a food processor. Add the butter and pulse, adding the reserved liquid (or water, if you run out) 1 tablespoon at a time, until the dip has the consistency of hummus. Place the dip in a bowl and let cool. Serve with pretzels, crackers, raw vegetables, or chicken tenders.