It's a source of pride that the small humans actually really like this meal. Little even asks to ‘test’ the doneness of the lentils while they're being simmered. Please note that this isn't a recipe, in the ‘exact quantities and timings’ sense — it's more a set of guidelines, a template, of how I make it. So the engineer types will find this annoying. Sorry.
Chop up the ingredients for the tomato sauce, as chunky or fine as you like. Heat some oil in a saucepan (make sure it is hot) and cook the onion first — till softened — then add the garlic, carrots, and celery. Give them a good stir for a few minutes before adding the herbs (if using), then the passata. Let it simmer for at least 20 minutes, if you can. If your lentils are pre-cooked, stir them into the sauce. If not, rinse and simmer the lentils for 10-15 minutes until they are cooked, then add them to the sauce and mix well.
Heat a couple of tablespoons of oil, then add a similar amount of plain flour, and stir it until it is throughly mixed, i.e. no dry flour. Give it a minute or two, then add a tiny amount of milk and stir until it joins the clump of roux you've just made. Keep adding small amounts of milk and stirring it until completely incorporated — it will get bigger and squelchier as it grows in volume. When it has the consistency of condensed milk, you can thin it out more generously. (Trying to smooth out clumps of roux in lots of milk isn't worth the effort, so patience is key.) Stir frequently. When it is at the consistency you're after, take it off the heat and add some cheese. If you're using an egg, beat it well and stir it into the sauce, the residual heat will cook it through.
Turn the oven on to 175-180°C.
At the bottom of whatever dish you're using to bake the lasagne, smear some tomato sauce. Add your first layer of lasagne sheets, followed by the tomato sauce and white sauce. Top it with grated cheese. Add the next layer of lasagne sheets and sauces (keep some white sauce back for the top layer), then more cheese. Place your final layer of lasagne sheets on top, smear on the rest of the white sauce, then top it with a generous amount of cheese.
Bake it for around 45 minutes, until it looks browned around the edges and bubbly.
28th January 2021