Slice the pork tenderloin into medallions and place them in a bowl. Season with salt, black pepper, and 2 tablespoons of oil. Toss to coat evenly.

Heat 4 tablespoons of oil in a large skillet over high heat. Once very hot, add the pork medallions and sear until golden on both sides, working in batches if needed. Transfer the pork to a bowl and set aside.

Wipe out any burnt bits from the skillet. Add the butter and let it melt, then add the mushrooms. Cook until all the moisture evaporates and the mushrooms turn golden. Transfer to a bowl.

Add the chopped onion to the skillet and cook until soft and lightly golden, about 7 minutes. Stir in the garlic and Dijon mustard and cook for 2 minutes until fragrant.

Sprinkle in the flour and stir until fully incorporated. Slowly pour in the cognac, stirring constantly. Let it simmer for 3–4 minutes so the alcohol cooks off.

Add the broth, salt, black pepper, thyme, and bay leaves. Stir to combine, then return the pork to the skillet. Cover and simmer gently over low heat for 40 minutes.

Remove the lid and stir in the heavy cream. Add the mushrooms back to the pan and simmer for another 15 minutes. Leave uncovered for a thicker sauce, or cover for a slightly looser sauce.

Remove bay leaves, garnish with fresh parsley, and serve warm.