How to Make It
Preheat broiler with oven rack 6 inches from heat. Process cauliflower florets in a food processor until finely chopped.
Bring 1 1/2 cups of the broth to a boil in a large saucepan over high heat. Whisk in cauliflower and cornmeal. Reduce heat to medium. Cook, whisking often, until thickened, 3 to 4 minutes. Remove from heat; stir in Cheddar.
Place tomatoes in an ovenproof skillet; mist with cooking spray. Broil, stirring after 2 minutes, until skins are blistered and tomatoes pop, about 5 minutes. Transfer to a small bowl.
Melt butter in same skillet over high heat. Add mushrooms, salt, and pepper; cook, stirring, until lightly browned, 6 to 7 minutes. Add tomatoes, coffee, and 1 3/8 cups of the remaining broth. Simmer until liquid is reduced by half, about 4 minutes. Stir together cornstarch and remaining 2 tablespoons broth. Add to mushroom mixture. Cook, stirring constantly, until mixture thickens, about 1 minute. Remove from heat; add scallions. Divide cauliflower mixture among 4 shallow bowls. Top with mushroom mixture.