French green lentils (Puy lentils) make a hearty base for this vegetarian shepherd’s pie. They may be slighter harder to find than other lentils, but they’re worth the extra effort. Unlike brown or red lentils, green lentils retain their shape and texture after cooking, which means they stand up well to a long simmer and this rich potato topping. Store-bought vegetable stock can vary greatly so be sure to buy one with a pleasant flavor that isn’t too sweet. (Note: Parmigiano-Reggiano cheese…
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