Coat slow-cooker bowl with nonstick cooking spray. Place 1 long sheet of nonstick foil in bottom of slow cooker bowl, with ends hanging over handles.
Whisk together flour, pumpkin pie spice, baking soda, baking powder and salt; set aside.
Beat together butter and brown sugar on high speed for 1 minute. Beat in egg. Scrape down sides of bowl and, on low speed, beat in buttermilk (mixture will look curdled). Beat in applesauce. Add flour mixture to bowl and beat on low speed until combined.
Spread batter into slow cooker. Place a clean dish towel over slow cooker then put cover on top. Cook on HIGH for 2 1/4 to 2 1/2 hours or until toothpick inserted in center comes out clean. Use foil handles to lift cake out of slow cooker. Cut into slices. Garnish with caramel sauce, whipped topping and pecans, if desired.