Filling: In a saute pan, melt the butter. Heat it to medium high heat and saute the cabbage until tender. Add the salt and sugar and stir to dissolve. Add the raisins and cook a few minutes to reduce and thicken any juices. Stir in the walnuts and spread on a sheet pan to cool.
Strudel: Preheat the oven to 375 degrees.
Line a sheet pan with parchment paper. Transfer 1 sheet of phyllo to a sheet pan. Using a pastry brush, brush the phyllo with butter. Sprinkle with 1/3 of the sugar and 1/3 of the chopped walnuts. Repeat with the 2 remaining sheets of phyllo. Reserve the remaining melted butter and sugar. Turn the sheet pan so that the phyllo is horizontal to your body. Spoon the cooled cabbage filling 2 inches in from the left hand edge of the phyllo, working from top to bottom, leaving 2 inches bare at the top and bottom. Turn the sheet pan 1/4 turn and roll up the pastry to encase the filling, forming a log. Move the log to the center of the sheet pan and tuck the ends under to keep the filling from oozing out. Brush the surface with melted butter and sprinkle with sugar. Bake until golden brown, about 30 minutes. Let cool 10 to 15 minuets on the pan. Using a serrated knife cut carefully into sections and serve warm.