Preheat oven to 356°F / 180°C. Wash the plums, remove the pits, and slice them into smaller pieces so they’re easy to layer on the pastry sheets.
Melt half the butter in a frying pan. Add the breadcrumbs and stir until golden and fragrant. In a separate pot, melt the remaining butter gently over low heat for brushing the pastry.
Spread out a clean kitchen towel on the counter and place the first sheet of phyllo on top. Brush lightly with melted butter, then cover with a second sheet. This creates a sturdier base that bakes up extra crisp.
Brush the second sheet with more butter and sprinkle over about one-fifth of the toasted breadcrumbs, keeping the rest for the other strudel rolls.
Scatter some of the sliced plums (1/5) on top of the breadcrumbs, leaving space at the shorter ends of the pastry so you can fold them in. Sprinkle sugar over the plums, adjusting the amount to your preferred sweetness.
Dust the plums with cinnamon, then fold the short edges of the pastry over the filling to keep the juices inside as it bakes. Roll the strudel up from the long side, tucking the filling in as you go. The kitchen towel is helpful to roll it easier.
Repeat the process with the rest of the sheets, plums, and breadcrumbs to make four more rolls. Line a baking tray with parchment paper, brush with a little butter, and arrange the strudels on top. Use the last of the melted butter to coat the rolls generously.
Bake for about 50 minutes with the fan on, until the strudels are golden brown and crisp.
Remove from the oven and sprinkle the tops lightly with water while they’re still hot. This keeps the pastry delicate and crunchy.
Dust with powdered sugar before serving. Plum strudel tastes best warm, especially with a scoop of ice cream or a dollop of whipped cream on the side. Enjoy!