Start by preparing the soffritto - that means throwing the the peeled garlic, carrot, fennel and onion into a food processor and pulsing until you have a fine confetti. You can do this by hand with a sharp knife if you don't have a processor.
Put the Instant Pot onto Sauté and add the lamb mince. As it is much fattier than beef, cook until browned and if there is lots of oil, spoon it off and discard. Add the soffritto and cook for a couple of minutes until softened.
Add in the bay leaves, Vermouth, tomatoes, oregano, dill, parsley and the olives. Add in half a can of water (swish out any remaining tomato instead) and stir very well. Put the lid on and set the pot to Manual High for 15 minutes. QPR or NPR as desired. If very liquid, use Sauté to reduce it, stirring frequently.
In a medium saucepan, cook the butter, flour, mustard powder, and nutmeg together for 2-3 minutes stirring constantly to prevent it sticking or burning.
Gradually dribble in the milk a little at a time, whisking constantly over medium-high heat until all of it has been added. Continue to cook and whisk until thickened.
Preheat oven to 180˚C.
I like to do four layers of meat sauce, pasta and white sauce. And I usually make fresh pasta but you can use dried without changing the recipe. Use a dish about 20x30cm and layer up meat, pasta and white sauce. Top the final layer with the feta, crumbled into little chunks.
Cook for 45-60 minutes until cooked through, and the feta has melted just a little but caught in places. Allow to stand for 15-20 minutes before slicing and serving with plenty of salad on the side.
*= or if wanting to make fresh pasta, follow the instructions in my recipe for squash, celeriac and caramelised onion lasagne here.
This lasagne freezes well whole or sliced - I typically serve half and freeze half. Thaw in the fridge overnight and reheat slices for 20-25 minutes wrapped in foil in the oven until piping hot all the way through (on 180˚C). For a whole lasagne, you'll need to allow 30-35 minutes to reheat from chilled.
If not using an Instant Pot, simply cook the meat sauce on the hob. Cook for 45 minutes partially covered and if too liquid, reduce down before assembling.