Asparagus mousse with ham red onion salad

Name: Asparagus mousse with ham & red onion salad
Ingredients: 1 tbsp butter; 250g asparagus finely sliced; 300ml whipping cream; 200ml milk; ½ garlic clove sliced; handful baby spinach; 2 ½ gelatine leaves soaked in a little cold water; 1 egg white; 2 slices of air-dried ham such as prosciutto, diced; ½ red onion finely chopped; 2 spring onions finely sliced; 2 tsp olive oil plus extra for drizzling; squeeze lemon juice; small bunch watercress leaves picked