"This dish can be made in stages: traditional, with radicchio and lemon zest, or with radicchio, zest and roasted mushrooms on top," Rach says about the Spaghetti alla Gricia.
Preheat oven to 475°F. Arrange mushrooms and shallots on a parchment-lined baking sheet. Spray to coat or toss with oil, season with salt and pepper, and roast at center oven to crispy 15 minutes.
Bring water to a boil for pasta.
Place the guanciale in the freezer for 10 minutes. Once it's firm, slice it into thin ½-inch-long pieces.
Heat a large skillet over medium-high heat. Add EVOO, a turn of the pan, add guanciale or pancetta and render slowly over 7 to 8 minutes, reducing heat if necessary. You want all the flavor and a lightly browned product.
Salt the boiling water, drop the pasta and cook 6 to 7 minutes.
Add garlic to guanciale and swirl. Add 1 cup cooking water to pan.
Drain pasta.
Add radicchio (if using) to pan to wilt and add the lemon zest, pasta and cheese to toss and emulsify.
Serve pasta in shallow bowls and, if using, top with mushrooms and shallots.