Brussels Sprouts with Chestnuts

Ingredients

• 1 lb fresh chestnuts
• 1 lb Brussel sprouts, stem ends removed
• 2 tsp olive oil
• 2 green onions, thinly sliced
• 2 cloves garlic, finely chopped
• 1/2 tsp salt
• 1/2 tsp rosemary
• 1 tsp grated lemon zest
• 2 tsp cold, unsalted butter