In a medium saucepan, bring the stock, saffron and 1 cup water to a simmer over medium. Reduce the heat to low and cover.
In a round-bottom pan or a large skillet, heat the olive oil, two turns of the pan, over medium to medium-high. Add the pancetta and cook, stirring often, until the fat renders, 2 to 3 minutes. Add the onion, garlic and thinly sliced asparagus stalks. Cook, stirring often, until the onion softens, 2 to 3 minutes. Add the rice; stir 1 minute. Season with salt and pepper. Add the wine and stir until evaporated, 1 to 2 minutes. Add the broth mixture 1 cup at a time, stirring between additions, until almost absorbed, 18 minutes for al dente risotto. Stir in the asparagus tips during last 5 minutes of cooking. To finish, stir in the butter, then the cheese and season to taste.