Preheat oven to 400 degrees F.
In an oven-proof braiser or other low-sided oven-safe pan, melt 4 tablespoons of butter in the olive oil over medium high heat and add onion, carrots, and broccoli.
Stir and cook for one minute, add the water, cover, and cook for three minutes covered. Remove cover and add garlic and cook one to two more minutes to evaporate the water.
Stir in the flour to coat and lower to medium heat.
While vegetables are cooking, in a separate large saucepan over medium heat, add cream, sour cream, salt, mustard, pepper, nutmeg, Worcestershire sauce and hot sauce.
Once hot, add one cup of the cheddar, one cup of the Swiss and half a cup of the Parmesan cheese and whisk to melt. Once the cheese has melted into the sauce, remove from heat.
Also in a medium bowl, partially crush the Ritz and toss with two tablespoons of melted butter and the remaining Cheddar, Swiss and Parmesan.
Pour the cooked sauce over the partially cooked vegetables and flour mixture and stir to combine.
Top with the cracker mixture and bake uncovered for 15-20 minutes until browned and bubbly.
Serve immediately.