Lobster roll with lemon aioli - Le Coup de Grâce

Ingredients

• 2 medium lobsters, alive
• 250ml 1% sour cream
• Zest and juice from half a lemon
• 2 garlic cloves, finely chopped
• Salt and ground pepper
• 3 tablespoons butter + a bit for the buns
• 1/2 teaspoon fresh tarragon, finely chopped
• Pinch of salt
• Pinch of ground cayenne pepper
• 1 1/2 cup hearts of romaine salad, finely sliced
• 1 cup sharp cheddar, grated
• 2 submarine bread buns, sliced open lengthwise but still attached
• About 5 Tostitos chips, crushed in small crumbs