In a large pan on the stove, heat 1/4 cup of vegetable broth. Add the onion and garlic and sauté until translucent, about 6-7 minutes. Add more broth 1 tablespoon at a time if they start to stick.
*To cook lentils - add 1 cup of dry lentils to 2 cups of water. Cover and bring to a boil. Reduce heat to med-low and simmer for 15-20 minutes until lentils are tender, but still a bit firm, not mushy. Leftover lentils work perfectly in this recipe, so make them ahead of time to save time (and pots) on the day you make this Cottage Pie.