We like to bake asparagus at a high temperature (420 degrees) so that it cooks quickly but still stays slightly firm.  Depending on how thick the spears are, how much you cook at a time, and whether you open the oven door to check, it should take between 12-15 minutes for your asparagus to cook. You are looking for the stalks to become tender and the tips to begin to get a little crispy for this roasted asparagus recipe.