1. In a large pot of heavily salted boiling water, cook pasta until al dente or to desired firmness. Once pasta is almost done, be sure to reserve 2 cups of pasta water and set aside.
2. In a cast iron skillet over medium-high heat, place lemon halves face side down. Don’t move and cook until lemons are charred and golden brown, 2-4 minutes. Remove from heat and set aside. (If using a stainless steel pan, brush lemon halves with a small amount of oil before charring).
3. In a large pan or heavy bottom pot over medium heat, add 4 tbsp. butter and stir until it begins to foam. Add sage leaves and stir constantly until the butter becomes golden brown and the sage leaves are crispy. Be careful not to burn the butter. Remove sage leaves and set aside.
4. Reduce heat to low and add pasta directly into the pan. Squeeze lemon juice from the charred lemon halves directly into the pot and stir quickly to combine. Reserve lemon halves for serving.
5. Turn the heat off and add pasta water, the remaining 2 tbsp. butter, and parmesan cheese bit by bit. Stir quickly to meld until the sauce thickens. Add more pasta water as needed to achieve desired sauce consistency. Serve and garnish with additional parmesan, fresh cracked black pepper and crispy sage leave. Enjoy!