Stuffed Flank Steak with Creamy Caramelized Onion Sauce

As you can tell, caramelized onions are probably one of my favorite ingredients and add depth to a lot of meals, this one is no exception.








  • 1 Flank steak, pounded to 1/4″ thick


  • 1/2 C. balsamic vinegar
  • 1/2 C. olive oil
  • 1/4 C. brown sugar
  • 1/4 C. soy sauce
  • 1 tsp. pepper
  • 1/2 tsp. salt
  • 1 tsp. fresh rosemary
  • 1 tsp cayenne
  • 3 cloves garlic, minced


  • Basil, about a handful
  • 1 pkg. prosciutto
  • Shredded Mozzarella, about a cup


  • 2 large sweet onions, chopped
  • 2 Tbsp. butter
  • salt and pepper to taste
  • 2 cloves garlic, minced
  • 1 Tbsp. dijon mustard
  • 1/2 C. heavy cream
  • 1 1/2 C. white wine

Add all marinade ingredients to a large ziplock bag. Squeeze or stir to combine, add steak. Marinate at least 4 hours up to overnight.

Preheat oven to 350°

Start caramelizing your onions. Melt 2 Tbsp. butter over medium high heat and add a layer of onions, followed by a sprinkling of salt. Keep layering onions and salt until all the onions are in the pan. Let cook at medium for about 15 minutes without stirring (don’t worry about burning). Stir and lower heat to low. Cook until they are a rich brown color, 1 to 1.5 hours, stirring occasionally. Add garlic and stir, cooking until fragrant, about 30 sec. Remove onion mix and add to a food processor, pulse into a nice pulpy puree.

While onions are cooking, pull steak out of fridge and pat with paper towel, discarding remaining marinade. Lay the steak flat on a work surface with the grain running parallel to you (this way when you roll it and cut it, you will be cutting against the grain). Start with a layer of prosciutto, then a layer of basil, and finally sprinkling cheese over the top. Roll as tight as you can, then secure with cooking twine.

Heat 1 Tbsp. olive oil in an oven proof pan. Sear all sides of the steak until nice and golden brown, 8-10 minutes.

Place pan in oven and cook until thermometer inserted into the center reads 125°, about another 8-10 minutes. Pull out and let rest at least 10 minutes before slicing into 1/4″-1/2″ slices.

While steak is cooking, make your sauce. In same pan that you cooked the onions, melt 1 Tbsp. butter over medium high heat and add wine, let reduce by half. Reduce heat to medium and add onion puree, mustard, salt and pepper to taste. Cook 10 minutes, stirring occasionally.

Slowly stir in cream and cook until thickened, about 10 minutes.

Serve steak with sauce over top, or to the side for dipping.



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