Baked Portobello Mushroom Gratin

Ingredients

• 4 tablespoons butter
• 2 leeks, diced
• 1 celery root, chopped
• 3 large portobello mushroom caps, diced
• 1 tablespoon chopped fresh tarragon, divided
• 1 tablespoon chopped fresh chives, divided
• 1 cup panko bread crumbs
• 1 cup grated Gruyere cheese
• 1 ½ tablespoons all-purpose flour
• ¾ cup heavy cream
• 2 tablespoons water, or as needed

Step 1

Heat your oven to 400°F (200°C). In a frying pan, melt some butter over medium heat, then add the leeks and celery root. Let them cook gently for about 10 minutes until they start to soften. Toss in the mushrooms along with half of the tarragon and chives, and keep cooking until the mushrooms release their juices, which should take around 6 minutes.

Step 2

While that’s going on, mix the bread crumbs and Gruyere cheese together in a bowl. Once the mushrooms are ready, sprinkle the flour over the pan and stir it in. Slowly pour in the cream, stirring constantly until the mixture turns smooth and creamy, about 3 minutes. Then, add half of the bread crumb and cheese mix, stirring until the cheese just begins to melt—this should take a couple of minutes. Turn off the heat.

Step 3

Spoon the mushroom mixture into a baking dish, then sprinkle the remaining tarragon, chives, and bread crumb mixture on top. Add a little splash of water to keep things nice and moist. Pop it into the oven and bake until the cheese bubbles up and turns golden, about 10 minutes. Use a spatula to serve it up right away and enjoy!