A little steak sandwich with a horseradish zing should make eyes light up at the wedding reception.
Preheat oven to 425 degrees. Heat 1 tablespoon oil in a medium ovenproof skillet over high heat. Rub tenderloin with remaining tablespoon oil; season with salt and pepper. Place in skillet, and sear until meat is browned on all sides, about 2 minutes per side. Transfer to oven; roast until meat is desired doneness, 7 to 10 minutes for medium-rare. Transfer to a cutting board, and let rest 10 minutes.
Reduce oven temperature to 300 degrees. Using a small offset spatula, spread butter on each bread slice. Arrange bread on two baking sheets; place in oven to dry out and toast slightly, 5 to 7 minutes per side. Transfer to a wire rack to cool.
Combine creme fraiche and horseradish in a small bowl; season with salt and pepper. Place mixture in a pastry bag fitted with an Ateco #18 star tip.
Using a 2 1/2-by-1 1/2-inch rectangle cutter or serrated knife, cut out 2 rectangles from each bread slice. Using a sharp knife, thinly slice tenderloin into 24 pieces; place one on each canape, and pipe horseradish mixture on top. Garnish with thyme. Serve immediately.