Melt butter in a skillet over medium heat. Add shallot; cook and stir for 1 minute to soften. Add thinly sliced pears; cook until soft, about 5 minutes. Pour in white wine, brown sugar, thyme, salt, and pepper; increase heat to medium-high and simmer until the liquid has evaporated, and the pears have lightly caramelized, about 10 minutes. Set aside.
Cut a Brie-sized hole in the top of the sourdough bread to within 1/2-inch of the bottom. Cut the removed bread into pieces for serving, set aside. Score the Brie around it's edge, using a paring knife to cut 1/4-inch deep. Cut in half by looping an 18-inch piece of very thin string, or unflavored dental floss around the scored Brie and pulling the ends in opposite directions.
Place the bottom half of the Brie, cut-side-up, into the sourdough loaf. Top with 1/2 of the pear mixture and sprinkle with 1/2 of the slivered almonds. Place the remaining brie half on top, spread with remaining pear mixture, and sprinkle with remaining slivered almonds. Place on a baking sheet.
Bake in preheated oven for 45 minutes or until soft and gooey. Serve with sliced sourdough bread and crackers.