6 T. butter, divided
1 onion, chopped1 bosc pear, pealed, halved, cored, and sliced (I used 1 1/2 pears, diced)
3/4 c. packed, grated dry jack cheese (I couldn't find this so I used about 1/4 c. monterey jack, 1/4 c. sharp white cheddar, and 1/4 c. parmesean)
3 t. dijon mustard
1/2 t. salt
4 sheets frozen phyllo pastry, thawed (based on user reviews, I used eight sheets; however, next time I will use the phyllo shells... also highly recommended)
Melt 2 tablespoons of butter in heavy skillet over medium heat. Add onion and saute until brown, about 7 minutes. Add pear and saute another 3 minutes. Transfer onion and pear mixture to medium bowl. Cool slightly (I waited about 5 minutes) and then stir in mustard and cheese.
Melt remaining 4 tablespoons of butter (since I doubled the amount of phyllo, I needed about 8 tablespoons) in small saucepan. Place one phyllo sheet on work surface (cover remaining phyllo with damp kitchen cloth to keep from drying out). Brush with melted butter. Top with second phyllo sheet. Brush with melted butter (repeat two more times if using 4 layers of phyllo). Arrange half of the pear mixture in log alon 1 short end of the phyllo leaving 1 inch border at each end. Fold up sides and roll tightly into a log. Brush all over with butter. Transfer to a large baking sheet. Repeat with remaining phyllo, butter and pear mixture. (Strudels can be made 1 day ahead. Cover and refrigerate.)
Preheat oven to 375 F. Bake strudels until golden brown, about 18 minutes. Cool 5 minutes. Transfer 1 strudel to cutting board. Cut on diagonal into 12 pieces. Repeat with remaining strudel. Transfer to platter and serve.