How to Make It
Preheat oven to 350°F with rack in lowest position. Melt butter in a medium skillet over medium heat, swirling until golden and nutty smelling, 3 to 4 minutes. Pour into a bowl and let cool.
Toss pears, apples, flour, vanilla, salt, brown butter, and ¼ cup sugar in a large bowl.
Roll out one disk of piecrust on a lightly floured work surface to about 14 inches in diameter. Place in a 9-inch pie plate; trim dough to a 1-inch overhang. Fill crust with pear mixture. Roll out remaining disk to about 12 inches in diameter and lay over pears. Fold top edge over and tuck under bottom edge; crimp edge as desired. Cut a few vents in the top and brush with beaten egg. Sprinkle with about 1 tablespoon more sugar and freeze for 15 minutes.
Bake on bottom rack until deep golden brown and juices start bubbling through the cracks, 60 to 75 minutes. Let cool for at least 4 hours before slicing.