In a large pot or Dutch oven, melt butter over medium heat. Add onion and sauté 4–5 minutes, until soft and translucent. Stir in garlic and cook 1 minute.
Pour in white wine to deglaze, scraping up any browned bits. Simmer 1 minute. Add broth and pearl couscous, bring to a boil, then reduce heat and simmer 8–10 minutes, until couscous is almost tender.
Stir in butter beans, asparagus, and peas. Simmer 4–5 minutes, until asparagus is crisp-tender.
Remove from heat. Stir in pesto and season with salt and pepper. Ladle into bowls and top with shaved parmesan if desired.
Notes
Adjust seasoning after adding the pesto.
Store leftovers for up to 4 days in an airtight container in the fridge.
Couscous may soak up some broth as it sits, so add a splash if needed before reheating.