Toss the steak tips with the sea salt and 1/4 teaspoon of the ground black pepper.
Add 1 tablespoon butter to a large saute pan over medium-high heat. Once hot, add the beef to the pan, working in 2-3 batches to make sure you don't overcrowd the pan. Sear the beef for 1-2 minutes, until browned, then flip and cook an additional minute until browned. Remove from the pan and set aside.
Add another tablespoon of butter to the pan. Once melted, add the onion, garlic, and mushrooms and cook for 4-5 minutes, stirring occasionally, until the onions and mushrooms are browned and slightly caramelized. Remove the mushrooms from the pan.
Reduce the heat to medium-low and add 2 tablespoons butter to the pan. Sprinkle the flour over the butter and whisk to combine. Once smooth, pour in the broth slowly, whisking constantly. Let the mixture come to a bubble, then whisk in the coconut aminos, dijon mustard, lemon juice, and sour cream.
Reduce the heat to low, then stir the beef and onion and mushroom mixture into the sauce, and taste for seasoning. Add salt if needed. Let cook for an additional 5 minutes.
Garnish with parsley and serve over noodles!