In a medium saucepan, mix together granulated sugar, brown sugar, and cornstarch.
2. Stir in Rhubarb, orange juice and zest, and vanilla.
Cook over medium heat until bubbling and thickened.
Reduce heat to low, add cinnamon, and cook, stirring occasionally, for 10 minutes.
Remove pan from heat.
Cool completely. I even chill it in refrigerator.
Preheat oven to 400 degrees F.
Grease a baking sheet.
Unfold sheets of phyllo dough so they lay flat, cover with a damp kitchen towel. Cover a large cutting board with thick plastic wrap. Brash each of 4 sheets with melted butter, and sprinkle all over with walnuts.
3. Spread half of the filling along a longer side and using plastic wrap, roll up pastry tightly, like a jelly-roll, folding in the ends.
Repeat the same with the remaining 4 sheets phyllo, melted butter, walnuts, and rhubarb filling to make the second strudel.
Place both strudels seam-side down, on prepared baking sheet.
Brush the top with melted butter, with a sharp knife precut only the top of each strudel in 5 equal portions.
Bake until golden, about 15- 20 minutes. Transfer baking sheet to a cooling rack to cool for 15 minutes, then put strudels on the cutting board. Cool completely. Sprinkle with powdered sugar.
Serve hot or room temperature with ice-cream or whipped cream.
I like it with melted white chocolate.