The night before, cube the bread and set it in a large bowl to dry out - you want it to be the texture of day old bread - noticeably dry but not rock hard.
The day of, if the lentils have not already been cooked, do so now by thoroughly rinsing 3/4 cup lentils in cold water, then adding to a small saucepan with 1 1/2 cups veggie broth or water.
Cook over medium-high heat until a low boil is achieved, and then lower to a simmer and continue cooking uncovered for 20-30 minutes. Set aside.
Preheat oven to 350 degrees and line a 9x13 pan (or comparable sized dish) with foil or spray with nonstick spray. Also prepare flax egg and set aside.
Sauté onion and celery in the olive oil or vegan butter and season with a bit of salt and pepper. Cook until fragrant and translucent - about 5 minutes. Set aside.
To the bowl of bread, pour most of the broth then add the remaining ingredients (sage, cooked veggies, flax egg, and lentils) and mix with a wooden spoon. The key is to make sure it is about the consistency of a meatloaf. If it’s too dry, add more broth and mix again. If it’s gotten too wet, add more bread.
Transfer to the prepared pan and cover with foil. Bake at 350 for 45 minutes, then remove the top layer of foil so the top can brown. Increase heat to 400 degrees and bake for another 10-15 minutes, or until the top is well browned and crisp.
Remove from oven and let cool slightly before serving. Leftovers reheat well in the microwave or oven, though best when fresh.
This dish would be awesome with vegan mashed potatoes and vegan mushroom gravy!