Bring a medium sauce pot of generously salted water to a boil. Separate the pappardelle so the noodles don’t clump together during cooking. Add the pappardelle and cook, stirring occasionally, until just tender, 3 to 5 minutes. Drain the pappardelle, reserving 1 cup [1½ cups] pasta cooking water. While the water heats and the pappardelle cooks, prepare the vegetables.

• Peel and finely chop enough onion to measure ¼ cup [½ cup].
• Finely chop, press, or grate enough garlic to measure 1 teaspoon [2 tsp].
• Scrape off any seeds from the roasted red peppers; coarsely chop any large pieces.
• Rinse the butter beans.

In a large frying pan over medium-high heat, warm 1 to 2 teaspoons oil until hot but not smoking. Add the onion, season with salt and pepper, and cook, stirring occasionally, until starting to soften and caramelize, 2 to 3 minutes. Stir in the garlic and cook until fragrant, about 30 seconds.
Add the roasted red peppers, beans, artichoke hearts, and half the reserved pasta cooking water and season with salt. Bring to a boil, then reduce to a vigorous simmer and cook, stirring occasionally, until about half the liquid has evaporated, 3 to 5 minutes. Stir in the pappardelle and remaining pasta cooking water and cook until the sauce has thickened, 1 to 2 minutes. While the vegetables and sauce cook, prepare the remaining ingredients.

• Zest ½ lemon; cut the lemon into wedges for garnish. [Zest 1 lemon; cut the lemon into wedges; save the remaining lemon for another use.]
• Strip the parsley leaves from the stems; coarsely chop the leaves.

Remove the pan from the heat and stir in the lemon zest and parsley. Season to taste with salt and pepper.

Transfer the pappardelle and sauce to individual bowls, drizzle with the pistou, and serve with the lemon wedges.