A classic dish with a couple of twists - it's a vegetarian Cannelloni di Manzo - and it has a blue cheese pasta sauce, a besciamella (bechamel) sauce enhanced with some blue cheese.
Soak the lasagna sheets in water for at least 30 minutes or until needed.
Rinse the lentils and remove any stones or other debris.
Add to a saucepan with the 3 cups of water, one of the onions (halved), 4 cloves garlic (crushed with the side of a knife but still in one piece), and the bay leaves.
Bring to a boil then reduce to a simmer. Simmer for 30 minutes, or until the lentils are edible but still quite firm. They will cook some more in the next step.
Strain the lentils, removing the onions, garlic, and bay leaves.
Finely dice the other onion and remaining garlic cloves if using raw garlic as opposed to black garlic.
Heat the oil in a medium saucepan and sauté the onions and garlic until soft.
Add the finely diced mushrooms and sauté until softening.
Add the lentils, stout, tomato paste, diced black garlic (if using), salt and pepper, bring to the boil, then reduce to a simmer.
Simmer for 40 minutes. The liquid should reduce and thicken a bit.
Combine cornflour with a Tbsp of water and add to the saucepan, stirring to combine well, cooking for 10 more minutes.
Allow to cool. The mixture should further thicken as it cools.
Tomato sauce
Skin and dice the onion and garlic and sauté in the olive oil.
Wash, trim, and dice the carrot, celery and parsley.
Once the onion is soft and becoming translucent, add the carrot, celery, and parsley.
Sauté until vegetables are starting to brown.
Add the tomatoes, reserving the liquid.
Stir in the basil, red wine, and 1/4 cup of the reserved liquid.
Simmer for 30-40 minutes.
Use an immersion blender to make the sauce smooth. Add some more of the reserved liquid if it is too thick (depends on the tomatoes).
Set aside.
Blue besciamella sauce
In a saucepan melt the butter over a medium-low heat.
When melted, stir in the flour. Cook until the mixture starts to brown a little.
Slowly add the milk, whisking all the time.
Return to a boil, then reduce to a simmer for 10 minutes.
Add the nutmeg, salt, and parmesan and blue cheeses.
Set aside.
Assembly
Pre-heat the oven to 200 degC.
Spread the tomato sauce on the base of a baking dish. Should be about 1 cm thick.
Roll a large spoonful of lentil mixture into a lasagna sheet a place onto the tomato sauce in the baking dish.
Repeat until you run out of space or ingredients.
Spoon the blue besciamella sauce over the cannelloni - about half to one cm thick.
Sprinkle on the grated gruyere cheese.
Bake in the oven for 50 minutes. Grill it a bit longer if you need to brown the top a bit more.