A staple in regional cuisine, this potato gets the spa treatment and is topped with thin slices of grilled flank steak. We’re baking these potatoes instead of simmering them in water. Baking or roasting concentrates the natural sugars in the potato and caramelizes them just a bit adding a depth of flavor that isn’t present in boiled potatoes. The unfairly maligned russet is the potato needed for this soup. Its starch content helps to thicken this soup and makes it possible to absorb a bit of the milk and butter for a fuller flavor. While we are using milk in this soup, you can increase the creaminess by replacing ¼ cup or more of the milk with heavy cream.
To keep the milk from breaking (solids and liquids separating) while making this soup, we’re actually making a very thin white sauce. The addition of flour actually turns this soup into an emulsion, and emulsions are stabilized even during heating. If you are replacing some of the milk with cream, wait to stir in the cream until after you have heated the milk mixture through. Cream, with its high fat content, 36% compared to whole milk’s paltry 4%, doesn’t break, even when simmered. As the liquids evaporate, the cream just becomes thicker.
Flank steak, with it’s bold, beefy flavor also benefits from a soak in an acidic bath, notably a vinegar bath. Early in the day, prepare the flank steak by first trimming any thick portions of fat from the steak and then cutting an 1/8-inch deep crosshatch pattern on both sides of the steak. Flank steak’s muscle fibers run the length of the cut rather than top to bottom. When exposed to heat, these fibers will contract causing the steak to shrink and curl. The shallow cuts will also allow the marinade flavor to penetrate deeper into the muscle. The acidity in the marinade also compliments the creamy potato soup. Because flank steak is very lean, we’ll need to rub the surface with oil just before grilling. Use a mild vegetable oil or light olive oil here. Grill the steaks for 5 minutes a side on a medium high grill for medium, 4 minutes a side for medium rare, and 3 minutes a side for rare. Grilling past medium isn’t recommended for flank steak.
As purists, we’ve opted for just steak and potatoes here, but you could top this soup with a tomato relish of diced, seeded tomatoes, crumbled blue cheese and chopped chives, or complete the meal with a creamy Cesar salad. However you choose to serve it, this baked potato soup won’t disappoint.
Instead of the appearing as the flank steak’s plucky sidekick, the baked potato takes center stage in this hearty soup.
Baked Potato Soup with Flank Steak
The Marinade
- ¼ cup balsamic vinegar
- ¼ cup Worcestershire sauce
- ¼ cup lite soy sauce
- 1 tablespoon dijon mustard
- 1 tablespoon finely minced garlic
- fresh ground salt and pepper to taste
- mild vegetable oil for grilling
Mix all the ingredients except the oil in a shallow dish. Slice a very shallow crosshatch pattern on both sides of the flank steak or steaks. Cover both steaks in the marinade and allow to sit for at least 4 hours.
The Soup
- 4 large russet potatoes, baked, peeled, and mashed
- 1 medium Spanish onion, diced finely, about 1 cup
- 4 tablespoons lightly salted butter
- ¼ cup all purpose flour
- 3 cups whole or 2% milk
- 2 cups chicken broth
- 2 teaspoons salt
- fresh ground pepper to taste
Wash the potatoes and pierce the skins. Bake the potatoes at 350°F for an hour or until tender all the way through. Remove from the oven and allow to cool for 20 minutes. Carefully peel the potatoes, discarding the skins. Mash the potato flesh. Set aside.
Preheat the grill to 600°F or HI when you start the soup. The grill should preheat for at least 20 minutes before cooking the steaks. Drain the marinade from the steaks and pat them dry. Oil both sides of the steaks and allow them to come to room temperature while the grill heats and you prep the soup. Melt the butter in a large dutch oven over medium high heat. Add the onions and sauté for 5 minutes or until they become translucent and fragrant. Add the salt and pepper, sauté for an additional minute. Sprinkle in the flour, stirring to combine. Cook the flour mixture for an additional 3 minutes, stirring constantly. Add the milk and broth, stirring to combine. Grill the steaks to taste while the soup heats, stirring occasionally. Remove the steaks from the heat and allow them to rest covered while the soup finishes.
Bring the soup to a simmer to thicken the broth. Add the potato flesh and stir gently breaking up any large potato chunks. Turn the soup to low to continue heating while you slice the flank steak across the grain. Ladle the soup and top with several thin slices of steak. Garnish with chives.