For the poached pears, place the wine and sugar into a large saucepan and leave to stand for a few minutes. Place the saucepan over the heat, bring to the boil and carefully stand the pears in the liquid (you may need to trim the bottoms of the pears to make a flat surface). Cover and simmer for 10-15 minutes, or until the pears are tender (the time will depend on how ripe the pears are.) Remove the pears with a slotted spoon and stand up in a dish to allow them to cool down. Meanwhile, rapidly boil the sauce to reduce to a thick syrup.
For the pain perdu, mix the eggs with the sugar in a large mixing bowl to dissolve the sugar. Gradually mix in the milk, vanilla extract and eau de vie de poire (or calvados or cognac). Divide this mixture between two large dishes.
Cut the crusts off the loaf and cut five slices about 2cm/1in thick. Cut these in half diagonally, then place all ten pieces into the egg mixture. Leave for five minutes, then carefully turn each piece over and leave for a further five minutes.
Preheat the oven to 170C/325F/Gas 3.
Heat a large knob of the butter in the frying pan and when foaming begin to fry the bread slices a few at a time. Allow two minutes per side before turning over. Each piece should be a good rich golden-brown. Remove the slices and place on a baking tray. Repeat this process until all the slices are cooked, remembering to wipe out the pan between each batch to stop the butter from blackening. The baking trays of pain perdu can now go in the preheated oven for 5-6 minutes.
For the rhubarb sauce, cut the rhubarb into lengths of about 2.5cm/1in and place in a saucepan with the caster sugar and a couple of tablespoons of water. Cook for 3-4 minutes, until just cooked, but still firm. Use a slotted spoon to remove a small quantity of the rhubarb and put this to one side while the remainder of the rhubarb cooks almost to a pulp - about another five minutes. Pass this mixture through a sieve into a bowl standing in cold water. When cooled, whisk in the icing sugar and add the reserved firm pieces of rhubarb.
To serve, place one pear on each plate beside a piece of pain perdu. Spoon some of the pear syrup over the pears and spoon the rhubarb sauce alongside, allowing some to fall over the pain perdu. Sprinkle the chopped mint over each serving and dust with icing sugar.