For the crumble, preheat the oven to 180ºC. Grease an ovenproof gratin dish with butter. In a large bowl, mix together the butter and the sugar, using your fingertips, until the mixture resembles breadcrumbs. Add the flour, mix until well combined, then set aside.
For the filling, place the whole pears into a pan, cover them with water and add 50g of the sugar. Bring the mixture to the boil, then reduce the heat to a simmer and simmer for 10-12 minutes, or until the pears are tender. Drain well and set the pears aside to cool. When the pears have cooled, remove the cores and finely chop the flesh.
Spoon a quarter of the pears in an even layer at the bottom of the greased ovenproof dish. Scatter a quarter of the blackberries over the pears, then sprinkle over two tablespoons of the caster sugar. Repeat the layering process until all of the pears, blackberries and sugar have been used up.
Sprinkle over the crumble mixture and bake the crumble in the oven for 20-25 minutes, or until the crumble is golden-brown and the filling is bubbling.
The Fine Tawny is drawn from a reserve of fine wood ports which have been aged for up to three years in seasoned oak casks, each holding about 650 litres of wine. The individual wines are then blended to guarantee consistency of quality and house style.