Pat the steaks dry with paper towel to remove any excess moisture. Then, brush lightly with olive oil and sprinkle both sides with a generous amount of salt and ground black pepper.
Preheat a large cast iron skillet or grill over medium-high heat. Cook the steaks for 4-5 minutes on each side until they're browned and reach your preferred level of doneness. Transfer to a warm plate and set them aside.
Melt 2 tablespoons of butter in the skillet. Add the shrimp, season with salt and pepper, and sear until they turn pink and are just cooked, about 2 minutes. Then, transfer the shrimp to a bowl and set aside.
Deglaze the skillet with a small amount of chicken stock, then add the remaining stock and heavy cream and bring to a gentle simmer.
Add the Boursin cheese and stir it with a spatula. As it warms up, it will melt into the stock and form a sauce. Stir in the Dijon mustard, then let the sauce simmer for a few minutes to thicken. Keep in mind that it will thicken further as it cools down. Season with salt and pepper.
Return the shrimp to the pan, sprinkle with parsley, and stir to combine.
Serve with steaks.