Bring the sugar, maple syrup and water to the boil in a wide pan without stirring. Reduce the heat and simmer, swirling the pan occasionally until a light brown caramel has formed. Add the nuts, mix, spread immediately onto a sheet of baking paper, leave to cool. Roughly chop the nut brittle.
Mix the pears, maple syrup, lemon juice, vanilla pod and seeds in a pan, cover and cook over a medium heat for approx. 15 mins. until soft. Puree the pears until smooth, leave to cool. Heat the cream and sugar in a pan. Pour half into the egg yolk, whisk thoroughly. Pour the mixture back into the pan and simmer over a medium heat, stirring constantly, until the mixture thickens and turns creamy. Pour the mixture through a sieve into a stainless steel bowl, leave to cool. Add the pear puree and yoghurt, mix together.
Freeze the ice cream mixture for approx. 6 hrs., stirring at least 4 times with a whisk. Add 3/4 of the nut brittle with the final stir. Plate up the ice cream, sprinkle with the remaining nuts, drizzle with maple syrup.