Blue Potato Strudel with Brown Butter Herb Sauce

2 Lbs blue potatoes, peeled and cut into 1/8 inch slices (if necessary, substitute Yukon Gold)
1 3/4 Tsp salt
2 onions chopped
2 large eggs, beaten
3 Tbsp flat leaf parsley chopped
12 sheets phyllo dough
6 Tbsp olive oil
Fresh ground black pepper
3/4 Lb butter
3/4 cup Ricotta cheese
3 Tbsp fresh chives, chopped
3 Tbsp mixed herbs, chopped (chervil, tarragon, chives, parsley)

In a large deep frying pan, heat the oil over moderate heat. Add potatoes, 1 1/2 tsp. salt and 3/4 Tsp pepper and cook, stirring frequently, until the potatoes are tender and golden brown (20 to 25 minutes). Transfer to a large bowl.

In same pan, melt 4 Tbsp. butter over moderate low heat. Add onions and cook, stirring occasionally, until very soft (about 8 minutes). Add to potatoes and cool slightly. In a food processor pulse potato mixture in batches until chopped coarse. Return to the bowl, stir in the eggs, ricotta, chives, and parsley until just combined.

Melt 8 Tbsp butter. Lay one sheet of phyllo dough on work surface, a short end toward you. Keep the remaining phyllo covered with a damp towel. Brush the phyllo sheet lightly with some of the melted butter and top with another sheet. Put 1/2 cup potato filling in the bottom left hand corner. Fold up like a flag, maintaining the triangular shape. Brush once more with butter. Put the triangle, seam side down, on a baking sheet. Repeat with the remaining phyllo sheets and filling.

Heat the oven to 350 degrees. Bake the triangles until crisp and golden brown, about 35 minutes.

Melt remaining 1 1/2 Tbsp butter in large frying pan over moderate heat. Add remaining 1/4 Tsp salt. Cook until butter turns golden brown, about 4 minutes. Remove from heat and cool slightly. Stir in herbs and a pinch of pepper. With a serrated knife, cut the triangles in half. Put one half in the center of the plate and lean the other half against it so that you see the filling. Drizzle the butter sauce around each serving.

Chef's tip: Phyllo dough is usually sold frozen. To make working with this delicate pastry easier, thaw it slowly in the refrigerator. Then let it come to room temperature, still sealed so that it is less likely to crack. Make it a day ahead and cook right before serving.