First, prepare the sauce:
In a small saucepan, melt the butter in the oil.
Add the shallots and garlic. Season with pepper to taste.
Cook for 3 to 4 minutes, until golden brown.
Deglaze with the wine and reduce until almost dry.
Add the broth, rosemary, and reduce by half, about 4 minutes.

Add the cream, whisk a little, and reduce by half again.
Add the cheese and whisk until melted.
Add the mustard, mix a little, and strain to keep only the creamy and smooth sauce. Reserve warm.

Season the pork medallions with salt and pepper. Reserve.
In a frying pan, melt the duck fat over medium-high heat.
Sear the medallions for 2 minutes on each side.
Serve 4 to 5 medallions per guest and drizzle with the smoked Gouda sauce.