Preheat the oven to 350°F. To make the shortbread crust, combine the butter, flour, brown sugar, salt and egg in the bowl of a food processor and pulse until the mixture just comes together into a crumbly dough.
Sprinkle the dough over the bottom of a 13-by-9 inch baking pan and use a metal spatula to press evenly into the pan. Bake the shortbread until golden, about 20 minutes.
Meanwhile, make the filling. Melt the butter in a heavy saucepan over medium-low heat. Stir in the brown sugar, maple syrup, cream and pumpkin pie spice and bring to a simmer. Simmer for 1 minute, then stir in the pecans and candied bacon.
Remove from the heat. Pour the pecan mixture evenly over the hot shortbread. Bake until the pecan mixture is bubbling, about 20 minutes.
Remove from the oven and cool on a wire rack. When cool, cut into 48 (about 1- by 2-inch) bars. The bars will keep in an airtight container for up to 5 days.