Preheat and oven so you can set the broiler on high later. Start with heating the cream, salt, pepper, and onion powder in an oven-safe skillet over medium heat on the stove.
Step 2
Bring the cream to a simmer, then reduce to a low heat. Whisk in the dill and cheddar cheese. Whisk until the cheese has melted.
Step 3
Keep the cheese sauce gently bubbling as you slice the portabella into 8-10 pieces. Press the mushroom slices into the cheese sauce.
Step 4
Transfer the skillet to your oven with the broiler set on high. Broil for 5 minutes. Allow the skillet to cool for 2-3 minutes before serving.