Open Sandwich of Chicken, Avocado and Tarragon

• 1 slim baguette
• 2 chicken breasts roasted and cold
• 50g (2oz) butter
• 2 ripe avocados
• 4 tablespoons mayonnaise
• A small bunch of fresh tarragon
• 1 lemon
• Black pepper

Reserve 10 tips from the tarragon and chop the rest. Stir the chopped tarragon into the mayonnaise with a squeeze of lemon and a few turns of black pepper. Cut 10 slices about 1cm thick from the baguette at an angle and butter them. Slice the chicken. Peel, halve and stone the avocados and cut them into thick slices. Arrange slices of chicken and avocado on to the bread slices and place a spoonful of mayonnaise on top of each one. Garnish with the reserved tips of tarragon on each one and arrange the sandwiches on a plate. Decorate with lemon wedges.