Technical Stages :

• Cook the spinach in salted boiling water for 3 minutes, then transfer immediately to cold water.
• Repeat the procedure with the tarragon for 1 minute.
• Bring the chicken stock to a boil and reduce to the equivalent of 2 table spoonfuls.
• Add the spinach and filter through a chinois, packing the herbs.
• Combine the juice with the butter, whisking.