Add all of the steak ingredients to a large bowl EXCEPT the ground beef. Whisk together with a fork until thoroughly combined. Add the ground beef and combine with your hands.: Right away you will notice the blend of ketchup, Dijon mustard , bouillon and seasonings smelling tangy and savory, a prelude to the finished patties. Use your hands to fold gently so the mixture becomes cohesive without overworking it, which keeps the texture tender. A common mistake is squeezing too firmly, which yields dense patties, so handle the mix lightly. If the mixture feels dry, a small splash of broth can help, but avoid adding too much liquid because that will make the patties loose and prone to falling apart while searing.
Divide the mixture into 4 equal portions, and pat firmly into oval patties around 3/4”-inch thick. Make a shallow depression/dimple in each patty so the outer border is about a 1/4 inch higher than the middle (see pics). This will help them cook more evenly/quickly/not bulge.: When you press the patties, you should feel them hold their shape but still yield slightly under pressure, signaling the right texture. The dimple is subtle but crucial, preventing the center from puffing up as the proteins contract. If patties are too thick the centers will take long to cook through, and if too thin they will overbrown and dry out. Keep them uniform so they finish at the same time in the gravy.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Sear the steaks on each side, about 3 minutes total. Transfer steaks to a plate (use along enough spatula! so they don't fall apart!) but leave the drippings behind. Note: the steaks will NOT be cooked through but will finish cooking in the sauce.: As the meat hits the hot skillet you should hear a lively sizzle and see a rich mahogany crust form within moments, signaling proper caramelization. That crust is packed with flavor and helps the patties hold juices. Avoid flipping too soon, which tears the surface and prevents a good sear. If the pan smokes excessively lower the heat slightly, and if the oil is barely shimmering raise it a touch so the crust develops properly.
Melt 1 tablespoon butter with 1 tablespoon olive oil over medium heat in the leftover drippings. Increase temperature to medium-high and add half of the mushrooms. Give them a stir to evenly coat in the butter then arrange mushrooms in a single layer. Cook mushrooms for 2-3 minutes per side or until golden.: When the mushrooms hit the fat they should hiss and begin to exude moisture, then slowly brown as the water evaporates. You will smell a deep, toasted aroma as the natural sugars caramelize, and visually the edges will take on a golden color. Crowding the pan will steam them instead of browning them, so work in batches. A common misstep is stirring too often, which prevents proper color development.
Remove mushrooms from skillet with a slotted spoon and repeat with remaining mushrooms; transfer all mushrooms to a plate.: The mushrooms will continue to release flavor into the pan as they rest, and removing them keeps the pan free for the shallots and gravy base. They should feel tender but still substantial to the bite. If any pieces start to burn, lower the heat for the next batch; burnt mushrooms give a bitter note that can dominate the sauce.
To the now empty skillet, melt 2 tablespoons butter with 1 tablespoon oil. Add shallots and sauté over medium-high heat for 2-3 minutes to soften.: As the shallots sweat they will become translucent and release a sweet, oniony perfume. This softening step builds the aromatic foundation for the gravy. If the shallots begin to darken too quickly, reduce the heat, because burned aromatics create an acrid taste. You want them softened and lightly golden, not crisp.
Reduce heat to low, add garlic and red pepper flakes and sauté for 30 seconds. Add flour and cook for 1 minute, scraping up the browned bits on the bottom of the pan.: The brief garlic sauté should release a fragrant, toasty scent without browning the garlic, which turns bitter. When you add the flour , it should bubble gently and smell slightly toasty, indicating the raw flour taste is cooking off. Scraping up browned bits incorporates concentrated flavor. A frequent error is cooking the flour too long or at too high heat, causing a pasty texture rather than a smooth thickener.
Slowly whisk in beef broth and all remaining gravy ingredients. Whisk until most of the lumps are gone.: Pouring the broth slowly while whisking prevents lumps and creates a silky texture; you will see the sauce transition from opaque to glossy as it smooths out. The aroma will shift to a rich, savory stew like scent. If lumps form, use a small mesh strainer or a vigorous whisk to break them up. If the sauce seems thin, continue to simmer gently to reduce and concentrate flavor.
Add the partially cooked steaks back to the skillet (use along enough spatula) and nestle into the gravy (it’s okay if most of the gravy covers them).: Nestling the steaks into the sauce allows them to finish cooking evenly while absorbing the gravy flavors. You will see the surface of the sauce ripple around the steaks as it simmers. Avoid overcrowding, which can cool the pan and slow the simmer; leave a little space so the liquid can circulate and reduce properly.
Bring to a simmer over high heat then reduce to medium. Cook for 5-7 minutes or until the internal temperature of the steaks reaches 160 degrees F, stirring occasionally around the steaks. If the gravy thickens too quickly, add additional broth.: The sauce should show gentle bubbles and a fragrant steam as it reaches a simmer. Use an instant read thermometer to check 160 degrees F internal for safety and juiciness. If the sauce thickens before the steaks are done, thin with splash of extra broth so the steaks finish in a silky sauce. Overcooking will dry the patties, so monitor temperature closely.
Once the steaks are done, stir in the mushrooms.: Returning the golden mushrooms at the end preserves their texture and concentrated flavor while letting them soak up the gravy. You will notice the dish gaining layers of aroma as the mushrooms mingle with the sauce. If you add them too early they can become overly soft, losing their pleasant chew.
Serve Salisbury Steaks topped with the mushroom gravy over mashed potatoes (the BEST), noodles or rice. Season with freshly cracked salt and pepper to taste.: The final presentation should be glossy and inviting, the gravy pooled around the steaks and seeping into mashed potatoes or over noodles. Freshly cracked salt and pepper at the end sharpens flavors and brings brightness. If the dish tastes flat, a tiny pinch of salt can elevate the savory notes instantly.
