Grilled artichokes and stems with lemon butter sauce

Ingredients

• 4 fresh artichokes
• 2 lemons
• 3/4 cup (180 ml) olive oil
• 1/4 cup (60 ml) white rice wine vinegar
• 3 cloves of garlic, crushed
• 2 tablespoons tarragon
• 1/2 cup (115 gram) unsalted butter at room temperature
• Freshly ground black pepper
• Sea salt