Pat dry the steak with paper towels and make sure it is at room temperature. Season the steaks with salt and pepper.
Heat butter in a skillet over medium-high heat. Sear the steaks for 3-4 minutes on each side (for medium-rare) or to your desired doneness. Remove and let rest under foil.
In the same skillet, sauté onion and garlic until soft with some butter.
Pour some water and let it simmer till it reduces by half.
Add in the heavy cream and mustard and let it simmer for 2 minutes.
Add in the chopped herbs and mix. Let it cook till thickened.
Pour in the mixture into a bowl and blend with a hand blender till smooth and clear of clumps.
Pour the sauce back into the pan and add the butter. Let it cook till smooth and thick.
Top your steak with this amazing sauce and serve the best with some French fries to have the whole French experience!