Cheesy Pull-Apart Broccoli with Cheddar

Trim broccoli stems so the crowns rest flat on a work surface and the florets are still attached. Pour water into a 9-inch glass pie plate or shallow dish and place the broccoli on top. Cover with plastic wrap and microwave on High until fork-tender and bright green, about 4 minutes. 

Place a rack 10 inches from broiler; preheat broiler. Line a small rimmed baking sheet with foil. Transfer the broccoli to the prepared sheet and drizzle with oil. 

Combine mayonnaise, mustard, garlic, salt and pepper in a medium bowl. Fold in white Cheddar and yellow Cheddar until combined. Using your fingers, spread the cheese mixture on top of the broccoli and fill in the areas between the florets. Broil until melted and golden on top, 1 to 2 minutes. Serve immediately.