Lentils can vary based on brand and age, so if yours have soaked up all of the cooking liquid and aren’t tender after 25 minutes, add a bit more water to keep them saucy and continue cooking until tender. For a smooth topping, make sure to cut the carrots smaller than the potatoes; carrots are denser than potatoes, so the cook time for the smaller carrot pieces will match the time for the larger potato chunks.