For the lamb: Preheat the oven to 250 degrees F.
Begin by unfolding the de-boned leg of lamb and placing in a large dish. Pour the lemon juice all over both sides of the lamb; this will help tenderize it.
To a roasting pan, add the carrots, celery and onions.
Place the garlic in a food processor and process until well chopped. Remove just under half of the garlic (about 4 cloves worth) and set aside for garlic butter. Add the rosemary and thyme leaves to the food processor and chop up well. Add the olive oil, salt and pepper. Pour the marinade over both sides of the lamb and massage it into the meat. Tie the lamb into a nice even shape with kitchen twine, and then place on the roasting pan on top of the vegetables.
Place in the oven and roast until desired point of doneness (internal temperature should reach 125 degrees F for medium-rare), 3 to 4 hours. When done, let rest for 12 to 15 minutes before carving into slices (against the grain) for sandwiches. Season the slices with salt before serving.
To make the jus, place the roasting pan over medium-high heat. Add the reserved thyme and rosemary stems and stir. Pour in the white wine, scraping up the brown bits at the bottom of the pan, and bring to a quick boil. Stir in the chicken stock and simmer for a couple of minutes while the lamb rests. Strain the liquid into a saucepan and keep warm until serving.
To make the garlic butter, place the reserved garlic in a small saute pan and set over medium heat. Add the butter and warm through. Cook the garlic until fragrant, 4 to 5 minutes, and keep warm until just before serving.
Preheat the oven to 375 degrees F.
Cut the sourdough loaf into 1-inch-thick slices and smear each slice of bread with the garlic butter. Place in the oven until toasted, about 10 minutes.
To assemble the sandwiches, smear each slice of bread with a little Fresno Chili Mayo on both sides then layer with a good heaping of sliced roast lamb. Top with a scoop of Fennel Brussels Sprouts Slaw and place top slice of bread on to form a sandwich. To serve, dip the sandwich in the jus.
Preheat the oven to 450 degrees F.
Spread the garlic and peppers on a small roasting dish and drizzle with a little olive oil. Place in the oven and roast the chiles until the skin blisters, 7 to 8 minutes. Remove from the oven, place in a bowl and cover with plastic so the chiles sweat. Allow to sit for 5 minutes, and then carefully peel the skins off and remove the stems and seeds.
In a blender, place the roasted chiles and garlic. Blend until smooth, and then add the egg yolks, lemon juice, sugar and some salt. With the blender running, slowly drizzle in the olive oil until the mixture emulsifies. Refrigerate the chile mayo until ready to use.
Remove the core from the fennel bulb and finely slice with a sharp knife or a mandoline. Repeat the process for the red cabbage. Finely slice the onion and the Brussels sprouts. In a large bowl, combine the olive oil, vinegar, sugar and lemon juice. Whisk together and season with salt and pepper. Fold in the shredded fennel, chopped fennel fronds and shredded Brussels sprouts. Mix together well, and then cover and place in the refrigerator for 15 to 20 minutes before serving so the vegetables soften and absorb the vinaigrette. Stir well before serving.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.