Remove tails from half of the prawns, finely chop and place in a bowl along with mayonnaise, crème fraîche, celery salt, tabasco, lemon zest and juice, mix to combine.
Divide the prawn mixture between four slices of bread. Top with remaining bread and using a sharp serrated knife remove crusts and cut each sandwich into four squares.
Spread a little extra mayonnaise along one side of sandwich and dip into the chopped chives. Serve immediately with chilled salmon roe, celery salt and extra peeled prawns.