Melt the butter in a cast iron skillet over a medium heat. Add the shrimp and sauté for about 5 minutes until the shrimp are mostly pink all over, stirring frequently. 

Add the white wine to deglaze the pan, then add the heavy cream, Dijon mustard, and Cajun seasoning. Stir well.

Continue to simmer for another few minutes, then add some grated Parmesan cheese. Allow it to melt into the sauce - it will thicken the sauce a little too - then serve, garnished with chopped fresh parsley and black pepper.