Flatiron Steaks with Creamy Juniper Sauce with Hash Browns

Bring a 4-quart pot of salted water (1 tablespoon salt for 3 quarts water) to a boil. Meanwhile, peel potatoes and cut into 3/4-inch pieces. Add potatoes to water and return to a boil, then boil 5 minutes. Drain potatoes and transfer to a bowl.
Meanwhile, cook onion in butter with 1/4 teaspoon salt and 1/4 teaspoon pepper in a 10-inch nonstick skillet over medium heat, stirring occasionally, until pale golden, about 5 minutes. Add to potatoes and mash gently, leaving larger lumps.
Add 2 tablespoons oil to skillet and heat over medium heat until it shimmers. Add potato mixture and pat out evenly. Cook, partially covered, without stirring, until underside is golden brown, about 10 minutes. Keep warm, covered, off heat.
Finely grind juniper berries in grinder. Pat steaks dry and season with 1 1/2 teaspoons salt, 1 teaspoon ground juniper (reserve remainder for sauce), and 3/4 teaspoon pepper (total).
Heat remaining 2 tablespoons oil in a 12-inch heavy skillet over medium heat until it shimmers, then cook steaks, turning once, 8 to 10 minutes total for medium-rare. Let steaks rest on a plate, loosely covered with foil, about 10 minutes.
Add shallot to skillet and cook over medium heat, stirring and scraping up brown bits, until shallot is softened, 5 to 7 minutes. Add wine and remaining ground juniper (about 1 teaspoon), then boil until most of liquid has evaporated, about 1 minute. Add broth and cream and boil until sauce is reduced to about 1 1/4 cups, 3 to 5 minutes. Add meat juices from plate and season with salt and pepper.
Serve steaks over hash browns and with sauce.