Prepare and Sear the Chicken: Pat the chicken breasts completely dry with a paper towel and season both sides generously with salt and pepper. Heat the olive oil and 1 tablespoon of the butter in a large, heavy-bottomed frying pan or skillet over medium-high heat. Once the butter is foaming, carefully place the chicken breasts in the pan. Be sure not to overcrowd it; cook in two batches if necessary. Sear for 5-6 minutes on each side, until golden brown and cooked through. Remove the chicken from the pan and set it aside on a plate.

Sauté the Aromatics: Reduce the heat to medium. Add the remaining tablespoon of butter to the pan. Add the chopped onion and cook for 3-4 minutes until softened and translucent. Add the minced garlic, chopped sun-dried tomatoes, dried oregano, and red pepper flakes (if using). Cook for another minute until the garlic is fragrant, stirring continuously to prevent it from burning.

Deglaze the Pan: Pour in the white wine or chicken stock to deglaze the pan. Use a wooden spoon to scrape up any browned bits (the fond) from the bottom. Let the liquid bubble and reduce by about half, which should take 1-2 minutes. This step is crucial for a deeply flavourful sauce.

Build the Cream Sauce: Reduce the heat to low and pour in the double cream. Stir everything together and bring the sauce to a gentle simmer. Let it bubble lightly for 2-3 minutes to thicken slightly.

Add the Cheese and Spinach: Remove the pan from the heat and stir in the freshly grated Parmesan cheese until it has completely melted and the sauce is smooth. What works best for me is adding the cheese off the heat, as this prevents it from becoming grainy or splitting. Return the pan to a very low heat and add the fresh spinach, a handful at a time, stirring until it has just wilted into the sauce.

Finish the Dish: Return the seared chicken breasts (and any juices from the plate) back to the pan, nestling them into the creamy sauce. Spoon some of the sauce over the top of the chicken. Let it all simmer together for another 1-2 minutes for the flavours to meld.

Garnish and Serve: Taste the sauce and adjust the seasoning with more salt and pepper if needed. Sprinkle with fresh chopped basil or parsley and serve immediately.