1. Dissolve the jelly in the boiling water and let it cool slightly. Beat together the mayonnaise, cream cheese and lemon juice until just combined. Stir in the cucumber, onion, peppercorns and fennel fronds; season to taste with salt. Lastly, stir in the jelly and mix well.
2. Spray a large ring mould or suitable 2L container (we used individual moulds) well with non-stick cooking spray. Divide the cucumber mixture between the moulds and refrigerate overnight.