Tender, juicy pork loin is a crowd-pleaser on any table, particularly when its enrobed in pie dough that's golden, flaky, and sealed up like a holiday package.
Pat pork dry with paper towels; season all over with salt and pepper. Sprinkle with coriander; rub onto pork.
Heat a large skillet over medium-high. Swirl in oil, add pork, and cook until browned on all sides, 3 to 4 minutes a side. Transfer to a plate; let cool completely. Pour wine into skillet, bring to a simmer, and cook, scraping up browned bits from bottom, until reduced to about 1 tablespoon, 2 minutes. Let cool completely.
Melt butter in a large skillet over medium. Add cut apples and cook, tossing occasionally, until softened and liquid has evaporated, about 7 minutes. Let cool completely.
In a small bowl, combine mustard, horseradish, chopped sage, and wine sauce. Reserve 1/4 cup of mixture, then brush remainder over surface of pork. Make a 2-inch-deep slit lengthwise all the way across top of loin; stuff with cooked apples.
Roll out one disk of dough on a lightly floured surface to a rectangle about 1 inch wider all around than pork. Place on a parchment-lined baking sheet. Center pork on dough; brush edges of dough with water. Roll out remaining disk of dough to a rectangle large enough to drape over pork with enough dough remaining for a border. Drape over pork; trim top and bottom doughs to a 3/4-inch border. Press and crimp edges with the floured tines of a fork to seal.
Preheat oven to 400 degrees. From dough scraps, cut two 12-inch-long, 3/4-inch-wide pieces. Arrange crisscrossed on top dough layer. Refrigerate 30 minutes. Brush egg wash over entire surface, then cut a few small vents in top of dough.
Bake 20 minutes; reduce temperature to 350 degrees and bake until pastry is golden and a thermometer inserted in middle of pork registers 138 degrees, about 5 minutes more. Let stand 30 minutes. Serve, garnished with crabapples, small apples, bay leaves, and sage sprigs, with reserved mustard mixture.
