Preheat the oven to 425°F. Line a large, rimmed baking sheet with nonstick foil or high-heat-resistant parchment paper and spray it with olive oil.
Olive oil spray
Wash the cauliflower heads, remove the outer leaves, and trim the very bottom of the core, keeping the core intact. Slice each cauliflower head into ¾-inch-thick slices. The outer slices will fall apart. Simply roast them as florets with the steaks. Plan on getting three steaks out of each cauliflower head.
2 medium cauliflower heads
Use paper towels to dry the cauliflower slices and florets. Arrange them in a single layer on the baking sheet. Spray their tops with olive oil and sprinkle them with half the seasonings.
1 teaspoon Diamond Crystal kosher salt, ½ teaspoon black pepper, 1 teaspoon garlic powder, 1 teaspoon paprika, 1 teaspoon coriander
Bake the cauliflower slices for 15 minutes. Remove them from the oven, carefully flip them using two wide spatulas, spray them with more oil, and sprinkle them with the remaining spices.
Return the cauliflower to the oven and bake it until browned and fork-tender, 10-15 more minutes. Serve immediately.
Video
Notes
Seasonings, especially salt, are guidelines. Adjust to taste.
Don't trim the core. Cauliflower stems are edible. Removing the core, even very carefully, will cause the steaks to fall apart. I remove the outer leaves and trim the very bottom of the stem, but I leave the core intact, and I find that it softens nicely and is delicious when baked.
You can keep the leftovers in an airtight container in the fridge for up to 4 days. Reheat them in the microwave at 50% power, covered, or in a 350°F oven, uncovered. You can also freeze the cooled leftovers for up to three months.