1. Trim tough core and cut leaves from cauliflower. Break into chunks, then whirl in a food processor until broken into tiny florets.
2. In a 12- to 14-in. frying pan, melt 1 tbsp. butter over high heat. Add panko and cook, stirring, until toasted, about 3 minutes. Add thyme leaves and toss to combine. Pour into a small bowl. Wipe frying pan clean.
3. Add remaining 3 tbsp. butter, the cauliflower, shallots, and 1 1/4 cups broth to same pan. Cover and cook over high heat, stirring often, until cauliflower is just tender, 3 to 4 minutes. Uncover and cook, stirring often, until liquid is absorbed, 8 to 10 minutes.
4. Stir in cream and heat until boiling. Remove from heat, sprinkle with cheese and truffle oil (if using), and stir until cheese is melted. If you want a creamier consistency, add remaining 1/4 cup broth. Season with salt and pepper.
5. Spoon into 4 wide pasta bowls and top with toasted panko.