Place the steak pieces between 2 pieces of plastic wrap
or parchment and pound to 1/4- inch thickness. Cut into 4 equal pieces, diagonally, against the grain.
In a small bowl, whisk
together 1 tablespoon of the olive oil
, balsamic vinegar, sugar and garlic. Put the steak into a sealable plastic bag with the marinade and let sit for 30 minutes at room temperature, or 1 hour in the refrigerator.
In the meantime, in a small bowl combine the blue cheese
and buttermilk with a fork, mashing until creamy. Stir in the Worcestershire and set aside.
Spray a large grill pan with cooking spray
and preheat over medium-high heat. Cut the onion into 1/4-inch rounds brush both sides with the remaining tablespoon of oil and grill 6 minutes per side. Separate into rings and set aside.
Remove the meat from the marinade and season both sides with salt and pepper. Discard the marinade
. Cook the meat in the grill pan
over medium-high heat for about 3 minutes per side for medium rare.
Arrange 3 radicchio
leaves and a pile of onions
on each serving plate. Top with a piece of steak. Drizzle
with blue cheese sauce and top with a sprinkling of parsley.