Step 1

Arrange a rack in the middle of the oven and remove any racks above it. Place a 10-inch cast-iron skillet on the rack, and heat the oven to 425°F.

Step 2

Quarter 1 pound cremini mushrooms (slice each quarter in half again for particularly large mushrooms). Push to the side of the cutting board or transfer to a bowl. Mince 4 cloves garlic; push aside. De-stem thyme leaves until you have 2 tablespoons leaves. Chop chives until you have 2 tablespoons.

Step 3

Whisk together 2/3 cup all-purpose flour, 2/3 cup whole milk, 3 large eggs, 1/4 teaspoon of the kosher salt, and several grinds black pepper in a medium bowl until no lumps remain, about 1 minute. Whisk in 1 tablespoon of the thyme leaves and 1 tablespoon of the chopped chives.

Step 4

Carefully remove the hot skillet from the oven and immediately add 2 tablespoons of the butter. Swirl to melt, making sure it coats the bottom and up the sides of the pan. Immediately pour the batter into the hot skillet. Sprinkle with 1/2 cup grated Parmesan cheese.

Step 5

Bake until golden and puffed and crispy on the edges, 18 to 20 minutes. Meanwhile, heat 2 tablespoons olive oil and 1 tablespoon of the butter in a large skillet over medium-high heat. Add the quartered mushrooms, toss to coat in the fat, and arrange in a single layer. Sear undisturbed until the bottoms are well-browned, about 3 minutes. Season with the remaining 1 teaspoon kosher salt and several grinds black pepper and sauté until browned and tender, about 5 minutes.

Step 6

Reduce the heat to medium. Add the minced garlic, remaining 2 tablespoons butter, and remaining 1 tablespoon thyme leaves and sauté 2 minutes more. Add 1/4 cup white wine or broth and cook until mostly evaporated, 2 minutes more. Remove from the heat and stir in a few handfuls of baby arugula, stirring to wilt slightly.

Step 7

At this point, your Dutch baby should be just about ready. When it’s done, pull it out of the oven and immediately top it with the mushroom mixture. Sprinkle with the remaining 1 tablespoon chives and more Parmesan cheese.