Mix the meats, mustard, garlic, and egg yolks together in a bowl.
Press the mixture into 3-inch round cookie cutters.
Dredge the patties in the flour, then sprinkle with salt and pepper.
Preheat a cast-iron skillet on high heat.
Add a splash of olive oil, then sear the patties until just kissed by the skillet, 1 to 2 minutes per side.
To a large skillet over medium-high heat, add a splash of vegetable oil and let get hot.
Add the shiitakes and let sear for a couple of minutes, then add the shallots and let cook for another few minutes before deglazing with the red wine.
Reduce by half, then add the stock. Keep cooking until thickened to your desired gravy consistency.
Add the red wine vinegar, then taste and season with salt and pepper.
Spread the blue cheese crumbles on a platter.
Place the steak haché over the blue cheese; spoon the gravy over the top.
Sprinkle with some fresh parsley and chives and hit it with freshly ground black pepper over the top.
