Prep your ingredients. Grate the Pecorino Romano cheese, shred the Brussels sprouts and slice the mushrooms. Set aside 1 tsp of Pecorino and black pepper for topping at the end
In a sauce pan, combine the salt and water (from ingredient list.) Heat on medium high heat until the water reaches a boil.
In the meantime, season a skillet with olive oil on medium high heat. When the oil is shimmering, add the vegetables to the pan. Sauté until the Brussels sprouts are bright green and the mushrooms are thoroughly brown and cooked through (5-7 minutes.) If the pan dries out while you are sautéing, add more olive oil so the vegetables don't burn. Remove the vegetables from the heat once they are cooked, and set them aside.
Once the water starts to boil, add the corn starch and whisk until thoroughly combined. Lower the heat to medium and continue whisking for 2 minutes, until the water slightly thickens. Make sure there are no clumps and that all of the corn starch is dissolved (that's why it's important to keep whisking through this process!)
Add the Pecorino Romano to the starchy water and whisk until a thick cheesy sauce begins to form. Make sure there are no clumps!
With a large spoon, stir in the crushed fresh black peppercorns until thoroughly combined.
Transfer the sauce onto the vegetables and stir, to make sure the vegetables are fully coated.
Top with a sprinkle of Pecorino Romano and crushed black pepper. Serve immediately.