Preheat oven to 400°F.
Boil water and salt it liberally. Cook pasta 5 minutes, cold shock and drain. Place in a buttered casserole dish and add cheddar crumbles.
Heat oil, 1 turn of the pan, in a large skillet over medium heat. Add pancetta, brown and render to lightly crisp; remove from pan and scatter around pasta. Add butter to pan and melt. When it foams, add garlic and stir 1 minute then add flour and stir until it bubbles. Whisk in milk, let it bubble then season with salt, pepper and nutmeg to taste. When sauce thickens to coat spoon, stir in half of the grated Parm and Gruyère. Remove sauce from heat, temper egg yolks with a ladle of sauce and whisk into sauce. Whisk the Dijon into sauce. Whisk egg whites until peaks form then fold in a quarter of them to the sauce. Fold in reminder and pour over pasta. Top with remaining cheese and parsley. Bake 20 minutes or until golden and puffed.
For the salad, bring a few inches of water to boil. Add salt then blanch snap peas for 2 minutes. Cold shock then split them lengthwise.
Whisk up Dijon with honey, grated shallot, garlic, lemon juice and vinegar. Whisk EVOO in a slow stream down the side of the bowl; season with salt and pepper.
Add the lettuces and fennel to a bowl along with the peas. Toast brioche to deep golden then pulse in a food processor to make large breadcrumbs. Toss breadcrumbs with salad and dressing to combine and serve.