For the custard, place egg yolks and sugar into a medium bowl and whisk to combine.
Place milk, cream and vanilla in a medium saucepan. Bring to a simmer then pour into the egg yolk mix, whisking continuously until combined.
Pour the mix into the saucepan and cook over low/ medium heat until thickened, stirring continuously. Place into a container and refrigerate to chill.
Preheat oven to 160°C. Halve pears and remove core.
Place pears cut side down into a baking tray in which they fit snugly. Pour over maple syrup, dot with butter and roast until just softened, for about 30 minutes.
Meanwhile, make the crumble mix. Place sugar, hazelnuts, flour and oats in a medium bowl. Pour over melted butter and stir until combined.
Turn over the pears, place a heaped mound of crumble on top and bake for 40 minutes or until golden.
