Put the sausage in the pot, if using, and select SAUTÉ. Cook the sausage until fully browned. If you chose not to use sausage, add 2 tbsp olive oil instead and wait for it to get hot.

Add the shallot, garlic, and anchovies and cook, stirring occasionally, until the shallot is tender and the garlic is fragrant but not browned, 3 minutes. Press Cancel.

Add the pasta, broth, red chili flakes, 1 cup cold water, 1/2 teaspoon salt, and several grinds of black pepper and stir so the pasta is mostly submerged. Place the broccoli rabe on top of the pasta mixture, but do not stir.

Lock on the lid, select the Pressure Cook function, and adjust to Low pressure for 5 minutes. Make sure the steam valve is in the “Sealing” position and that the “Keep Warm” button is off.

When the cooking time is up, quick-release the pressure. Remove the lid, add the crème fraîche and cheese, and stir to combine. Season with salt and black pepper. Transfer the mixture to a serving dish and let stand for 5 minutes before serving to allow the sauce to thicken slightly.