Champagne-Poached Lobster With Asparagus

Ingredients

• 6 baby leeks, trimmed and soaked in cold water to remove grit, tops reserved
• 250 ml Champagne (1 cup)
• 3 sprigs thyme
• 5 black peppercorns, coarsely cracked
• 1 lobster tail
• 1 bunch asparagus, trimmed
• To serve: salmon roe and chervil sprigs
• Champagne sauce
• 100 ml Champagne
• 25 ml Champagne or white wine vinegar
• 1 golden shallot, minced
• 100 gm cold butter, cubed
• 2 tsp lemon juice