1. Take the butter out of the refrigerator to soften. Bring a large pot of water to boil and salt it. (You want the water level no more than 3 inches from the top of the pot.) Get a large bowl of cold water handy by the stove and spread a clean kitchen towel out on your workspace.
2. Put the onions in a large dry skillet with a lid over medium heat. Cover and cook without stirring until the onions are dry and starting to stick to the pan, about 10 minutes. Add the olive oil and cook, stirring frequently, until the onions are browned in places, another 5 minutes or s,o then turn off the heat.
3. When the water in the pot comes to a boil, add half of the lasagna noodles, stirring almost constantly to keep them separate. (Tongs are a good tool for this; keep them closed at the beginning and open them later to gently poke around in the pot as they cook.) Keep cooking until they’re pliable but still underdone and intact, about 5 minutes. Carefully transfer the noodles to the cold water. Then drain them flat on the towel; it’s okay if they overlap a little or you can add another towel and layer more on top. Repeat with the remaining noodles. If you’re using water instead of stock, reserve 1 1/2 cups of the pasta cooking liquid.
4. Remove the onions from the skillet with a slotted spoon, then add the buckwheat to the skillet, put it over medium heat and cook, stirring constantly, until the kernels sizzle gently and smell like toast, 1 to 2 minutes. Add 1 1/2 cups of the stock (or pasta cooking liquid or water) and return the onions to the pan. Bring to a steady but gentle bubble, cover and cook, stirring once or twice, until the buckwheat is just tender, 7 to 10 minutes. Some liquid will remain. Fluff the mixture, taste, and add salt and pepper to taste.
5. Smear a thin layer of the softened butter into a 9- by 13-inch baking pan or dish. Spoon about 2 tablespoons of the buckwheat mixture onto one end of a lasagna noodle and roll tightly to enclose the filling. Transfer the roll to the prepared pan to start one of two lengthwise rows. Repeat with the remaining noodles. (You can cover the pan or dish – and the remaining butter – at this point and refrigerate both for up to a day ahead of baking.)
6. When you’re ready to bake, heat the oven to 400°F. Pour 1 cup of the remaining stock (or water) over the noodles and cover the pan tightly with foil. Bake for 15 minutes then carefully unwrap a corner of the baking pan and poke the middle of a noodle to see if it’s tender and moist with a teeny bit of liquid still covering the bottom of the pan. If not, add more stock or water if necessary, re-cover, and check again in 5 minutes.
7. While the noodle rolls are baking, use a fork or your hands to mash the butter with the cheese. Season with lots of black pepper. When the noodles are tender, remove the foil and dot the top with the cheese mixture. Return to the oven and bake uncovered until the butter and cheese melt, the remaining liquid is bubbly, and the noodles brown in places 10 to 15 minutes.

– Recipe developed by The Bittman Project for Bob’s Red Mill