Combine the first eight ingredients in a food processor and process until the egg yolks are foamy and lighter in color.
Add the cheddar cheese and horseradish and process again.
Slowly drizzle in the oil.
Transfer to a large mixing bowl and fold in the sour cream.
Preheat the oven to 375° and roast the cauliflower until just browned—about 30 minutes.
When finished, place the cauliflower in a large bowl to cool.
While the cauliflower is roasting, bring the potatoes to a boil in a large pot of salted water.
Lower the heat and simmer for 10 minutes, or until the potatoes are tender.
Drain and set aside to cool.
Once cool enough to handle (or not, if you’re Wilcox), slightly smash the potatoes into the bowl with the cauliflower.
While still hot, add the green onion, dill, lobster and the mayo mixture.
Spoon into a large baking pan or casserole dish and top with the crackers and a sprinkle of cheese.
Bake the casserole at 375° until the top is golden brown.