Sprinkle meat with salt and pepper.
Heat a large skillet, over medium-high heat, and add 2 tablespoons butter and/or oil.
When butter foam subsides or oil dimples, add meat; curve it into skillet if necessary.
Brown it well on all sides; total of 4 to 6 minutes.
Turn off heat, remove meat from pan; let it sit on a board.
When skillet has cooled a bit, proceed.
Cut meat into one inch-thick slices.
Once again turn heat to medium-high, add remaining butter and/or oil and, when it's hot, add pork slices to pan.
Brown on each side; about 2 or 3 minutes each.
Turn heat to low and remove meat to a warm platter.
Add 1/2 cup water to pan, turn heat to high, and cook, stirring and scraping, for a minute.
Lower heat slightly, add cream and cook until slightly thickened.
Stir in mustard, lemon juice or Calvados; taste and adjust seasoning.
Serve meat with sauce spooned on top, garnished, if you like, with parsley.
