Bring a medium pot of salted water to a boil. Drop the florets into the boiling water and cook for about 2 to 3 minutes, until very soft but not overcooked. Remove from the water and set aside to cool slightly. Transfer the florets to a food processor (you may need to do this in batches), along with the butter, yogurt and a few pinches of salt. Pulse until the florets go from grainy to very smooth, add a tablespoon more of yogurt if you need to, about 2 to 3 minutes. Salt to taste and set aside. 

Preheat oven to 400 degrees F. In a medium pot (you can use the medium pot from above and no need to wash it—you can just dump out the water), set over medium heat, heat olive oil. Once warm, add the onion and carrots and a few pinches of salt; cook until softened, about 2 to 3 minutes. Stir in the minced garlic cloves, a few pinches of freshly ground pepper and the dried herbs. Add the ground lamb and break it up into crumbles with a spoon; cook until mostly browned, about 3 to 5 minutes. Stir in the flour, tomato paste, chicken broth and worcestershire. Bring to a simmer, reduce the heat to low, cover and simmer slowly for about 10 to 12 minutes or until the sauce is thickened slightly. Lastly, stir in the frozen peas. 

Spread the mixture evenly in a 8-inch square dish. Top with the cauliflower mash and make a smooth topping. Bake for 25 minutes or just until the fill in begins to bubble.