Season the chicken breasts with salt and pepper on both sides.
In a shallow dish, mix the flour with the mustard powder, 1 tsp dried parsley, and dried thyme.
Dredge the chicken breasts in the flour to coat lightly on both sides. Shake off any excess.
Melt 1 tbsp butter and 1 tbsp olive oil in a large skillet over medium-high heat and brown what chicken breasts on both sides (about 3-5 minutes on each side). Transfer the chicken to a plate and keep warm.
In the same skillet, melt 2 more tbsp of butter and sautee the shallots and garlic for about one minute.
Pour in the wine and scrape the bottom of the skillet to remove any brown bits and pieces stuck to it. Bring to a boil and reduce by half, about 3 minutes
Add the heavy cream, 1 tbsp dried parsley, and 1 tsp dried oregano, and simmer, stirring constantly, until reduced by half again, about 3 more minutes.
Mix in the spinach and cook just until wilted. Adjust the seasoning and add more salt and pepper if needed.
Return the chicken to the pan, cover with the sauce, and cook just until heated through.