Add 1/2 cup brown sugar and 1/2 cup soy sauce to a zip-top bag.  Grate 2 cloves of garlic into the bag.  Zip the top closed and squish the bag to mix up the ingredients.

Rinse the steak and add it to the bag with the marinade.  Be sure the steak is completely covered.  Let this marinate overnight in the refrigerator (turn the meat once to coat both sides well).

To cook the Steak

Preheat oven to 350 degrees.

On stovetop heat a large castiron skillet to medium-high.  Add 2 tablespoons of oil or fat and brown the flat iron steak on both sides.

Insert a digital meat thermometer into the center of the steak and put the steak (in the castiron skillet) into the oven.  bake until the steak is 125 degrees in the center.

Let the steak rest on the counter tented with a piece of foil for 10 minutes before slicing.