Preheat the oven to 200C/400F/Gas 6.
Place the fennel, orange juice, thyme, vegetable stock and water into a pan and bring to the boil. Reduce the heat and simmer for five minutes, or until the fennel is just tender. Drain the fennel, discarding the cooking liquid, and pat dry.
Divide the sugar between two small blini pans and heat gently without stirring until the sugar caramelises and turns golden-brown. Remove from the heat, then divide the butter between the two pans and stir. Divide the fennel slices between the pans.
Cut out two circles of pastry slightly larger than the circumference of the pans. Place the pastry over the fennel, pressing down around the edges to enclose the filling.
Place in the oven and bake for 10-12 minutes, or until the pastry is golden-brown and cooked through.
For the Sauternes beurre blanc, place three of the scallop corals into a blender with the water and blend until smooth (you can freeze the remaining three corals for use in another dish, but only if the scallops have not been previously frozen).
Place the shallots, the coral purée and the Sauternes into a frying pan. Bring to the boil, then reduce the heat and simmer until reduced by half.
Whisk in the butter, a little at a time, until well combined, then season, to taste, with salt and freshly ground black pepper.
For the scallops, heat the butter in a frying pan until foaming. Season the scallops with salt and freshly ground black pepper, then place in the frying pan and cook on each side for 1-2 minutes, or until just cooked through.
To serve, carefully turn the tarte tatins out onto serving plates. Place three scallops onto the centre of each tarte tatin, then spoon the beurre blanc over the scallops and around the edge. Top with a sprig of fennel top.