1) Position a rack in the center of the oven and preheat to 200C/Gas 6.
2) Toss pears with the lemon juice and 2 tbsps of the caster sugar.
3) Melt butter in a small saucepan over medium-low heat. Set aside to cool, then skim the white foam off the surface and discard. Spoon the melted butter into a bowl, leaving behind the solids at the bottom of the saucepan.
4) Heat 2 tbsps of the reserved butter in a medium nonstick frying pan over medium-high heat. Add pear mixture and cook until pears start to give off juices. Add cranberries, cover, and reduce heat to medium-low. Cook until pears are crisp-tender, about 7 minutes. Remove from heat and stir in 2 tbsps of the bread crumbs; cool the mixture slightly.
5) Combine remaining 2 tbsps caster sugar with allspice and ginger in a small bowl.
6) Cut a piece of baking paper slightly longer than the filo sheets and lay it with a long edge parallel to you. Set the stack of phyllo sheets beside it and cover with a clean kitchen towel. Transfer one sheet of phyllo to the baking sheet with a long edge facing you. Brush with some reserved butter and sprinkle with 1 teaspoon each of the nuts and sugar mixture. Repeat with each remaining filo, replacing the towel as you work. Sprinkle remaining 2 tbsps bread crumbs over top sheet of phyllo.
7) Spoon the pear mixture across the filo about 2.5cm from the edge closest to you to make a mound, with a 5cm border at each end.
8) Using the baking sheet to help you get started, roll the filo tightly over the filling to make a log, seam-side down. Lift the baking paper with the strudel onto a baking tray.
9) Bake until golden, about 30 minutes. Transfer on the baking tray to a rack to cool. Trim ends with a serrated knife.
10) Dust with icing sugar and serve warm or at room temperature with creme fraiche or whipped cream, if desired.
Style: Cut the strudel into thirds, then cut each one of the pieces in half on an angle. This way, you get beautiful portions that stand at attention, showing off the layers and the filling.