Step 1

Heat oven to 400 degrees F.

Step 2

Heat half of the olive oil over medium-high heat in a large oven-safe pan (I use a 10-12" cast iron skillet, but a dutch oven or large flat-bottomed skillet work too)

Step 3

Season chicken thighs on all sides with salt and pepper.

Step 4

Gently add chicken thighs to the hot skillet and sear for 2-3 minutes per side until you have a nice, slightly brown crust. Don't worry if they're not fully cooked - they'll finish cooking in the oven.

Step 5

Remove seared chicken thighs to a plate and set aside. Return the skillet to the stove.

Step 6

Add the remaining olive oil to your skillet and turn the heat to medium.

Step 7

Add onion and garlic to skillet and sauté 2-3 minutes until onion has softened.

Step 8

Add diced potatoes to skillet and stir to combine. Cook another 2-3 minutes until potatoes have softened and developed some color.

Step 9

Add mushrooms to skillet and give everything a stir. Cook another 2-3 minutes until mushrooms have softened and reduced in size.

Step 10

Add the chopped fresh rosemary and another pinch of salt and pepper to taste. Stir to combine.

Step 11

Add chicken stock to pan a little bit at at time, stirring well between each addition to scrape off any browned bits from the bottom of the pan (that's where the flavor is!)

Step 12

Add the heavy cream to the sauce and stir to combine.

Step 13

Return the seared chicken to your skillet, nestling each piece into the sauce.

Step 14

Place the skillet in your hot oven and bake for 15-20 minutes until potatoes and chicken are each cooked through.

Step 15

Remove skillet from oven.

Step 16

Spoon 2-3 tablespoons of sauce out of the skillet (careful, it's hot!) and into a small bowl or measuring cup.

Step 17

Add cornstarch to bowl and whisk to combine. This is your cornstarch slurry.

Step 18

Slowly add cornstarch slurry back to skillet a bit at a time, stirring to combine. It can take a minute or two to thicken up - you may not even need the whole slurry, so just keep an eye on it!

Step 19

Add spinach and parmesan cheese to sauce and stir until cheese is melted. Garnish with an extra sprig of rosemary (optional) and serve immediately.