Start by boiling water for your pasta. Grab a large stockpot, fill it halfway with water, and bring to a boil over a high heat
Add the olive oil to a large pan, something big enough to hold your pasta once it’s cooked, and set over medium-low heat. When shimmering, add the onion and saute for 5 minutes
Once the onions are translucent, add the mushrooms and ¼ teaspoon salt. Increase the heat to medium and stir occasionally until the mushrooms have reduced in size and all extra liquid is evaporated and absorbed, about 5-7 minutes
Add the kale and cook until it’s wilted, which should take another 5 minutes
Add the brisket and brisket and broth cook for 3 minutes. Stir well and turn the heat back to a medium-low
Your pasta water should be rapidly boiling now. Add the remaining tablespoon of salt to the water and toss in the pasta. Stir well and cook al dente per the instructions on the packaging
Once the pasta is al dente, reserve ½ cup of pasta water and put aside, then strain the pasta over the sink into a colander. No need to rinse off the pasta!
Add 2 tablespoons of the reserved pasta water to the sauté pan then add the pasta. Give it a really good stir to evenly distribute the sauce. Sample your sauce and if you’d like it to be saltier or saucier, add more pasta water to taste. Before serving the pasta add the lemon juice and give it another stir
Ladle into four bowls, topping each bowl with a generous amount of parmesan and red pepper flakes, if desired!