Heat oven to 200C/fan 180C/gas 6. Punch out a circle from the centre of each slice of bread using a 10cm round cutter and roll flat with a rolling pin. Brush circles with the melted butter on each side, then press into 8 individual tart tins. Lift onto 2 baking sheets and bake for 10 mins or until tinged with gold at the edges. Carefully flip the cases out from the tins so they are upside down on the trays, then put back into the oven for 5 mins or until crisp and dry. Leave
to cool. Can be kept in an airtight tin for up to 3 days.
To start the sauce, put the vinegar, peppercorns and bay leaf into a small pan and bring to the boil. Simmer for about 5 mins or until reduced to about 1 tbsp. Take off the heat, then strain out bay leaf and peppercorns. Will keep covered in the fridge for up to a week.
Halve avocados, stone and peel. Thinly slice avocado, put into a bowl and gently toss with a squeeze of lemon juice. Can be kept covered in the fridge for up to 2 hrs before serving. When ready to serve, put the avocado and a little rocket into each case, then top with crabmeat. Tip vinegar reduction into a tall, narrow jug, then add the egg yolks. Melt the butter in a pan over a medium heat (don’t boil), then add to the jug. Put a stick blender right to the bottom of the jug, turn on and draw very slowly up through the butter. The sauce will thicken as the yolks and butter meld together. Add herbs, season, then add a dash of lemon juice to bring out the herby flavour and cut through the butteriness. Spoon the hollandaise generously over each tartlet so it oozes over the crab. Serve at once.