1. Place a rack in lowest part of oven and heat to 425 degrees. Grease a baking sheet and set aside.
2. Halve cauliflower crosswise and trim any remaining leaves and pieces of stem. Working with one half at a time, place cauliflower cut side down and slice lengthwise into 1/2"-thick planks. Transfer to prepared baking sheet, working carefully to keep pieces from falling apart.
3. In a small bowl, whisk mustard, oil, spices, and salt until combined, then brush evenly over both sides of cauliflower. Bake until bottom is browned, 12 to 15 minutes, then flip and continue to roast until cauliflower is fully tender and browned on second side, 10 to 12 more minutes.
4. To assemble sandwiches, divide cheese over four slices of bread, then top with sauerkraut and cauliflower. Spread dressing over remaining bread slices and place on top of cauliflower.
5. Melt half of butter in a large skillet over medium, then add two sandwiches and cook, pressing on bread occasionally, until golden brown, about 3 minutes. Flip and continue to cook until cheese is melted and second side is browned, about 2 more minutes. Transfer to a plate and cover loosely to keep warm, then repeat with remaining butter and sandwiches.
Source: Hannaford fresh Magazine, March-April 2021