Preheat oven to 450° F. On a baking sheet, toss the potatoes and brussels sprouts with 2 tablespoons olive oil. Season with salt and pepper. Roast for 15 minutes, or until tender. Meanwhile, whisk together the honey, mustard, garlic, chili powder, cayenne, and 2 tablespoons olive oil. Season with salt. Place the salmon on a plate and spoon the sauce evenly overtop. Remove the vegetables from the oven. Add the salmon to the baking sheet. Add the butter to each filet. Bake for 10 minutes, or until the salmon reaches your desired doneness. During the last minute, switch the oven to broil and broil until lightly charred. Watch close. To make the dressing. Combine all ingredients in a blender and blend until smooth. Add 1/4 to 1/2 cup water to thin the dressing. Taste and adjust the salt.As soon as you pull everything out, drench the vegetables in dressing, then top with extra parmesan. Serve the salmon and any sauce left on the pan over the potatoes. Add more dressing. Enjoy!