Heat the olive oil in a large Dutch oven over medium-high heat. Add the sliced sausage in a single layer and cook for 2–3 minutes per side, until nicely browned around the edges. Transfer to a plate and set aside, leaving the flavorful browned bits in the pot.

Reduce the heat to medium and add the butter. Add the onion, carrots, celery and red bell pepper and cook for 5–6 minutes, stirring occasionally, until the vegetables begin to soften. Add the garlic and cook for another 30 seconds, just until fragrant.

Stir in the smoked paprika, Italian seasoning, thyme, red pepper flakes, salt and black pepper. Cook for about 30 seconds, stirring constantly to release the flavors of the seasonings.

Add the potatoes and stir well. Pour in the chicken broth, scraping the bottom of the pot to release any browned bits. Bring to a gentle boil, then reduce the heat to medium-low, partially cover and simmer for 12–15 minutes, until the potatoes are fork-tender. Avoid overcooking so the potatoes keep their shape.

Reduce the heat to low. Stir in the heavy cream, Parmesan and Dijon mustard, then return the browned sausage and any juices from the plate to the pot. Simmer gently for 4–5 minutes, stirring occasionally — do not allow the stew to boil vigorously after adding the cream.

Add the fresh spinach and stir until wilted, about 1–2 minutes. Taste and adjust the salt and black pepper as needed. If the stew is too thick, add a splash of chicken broth; for a thicker stew, gently mash a few potato pieces against the side of the pot and stir them back in.

Remove from the heat and let the stew rest for 5 minutes. Finish with the chopped parsley and a little fresh dill if desired, and serve warm.