Heat oven to 350° F. Combine the flour, confectioners' sugar, and butter in the bowl of a food processor. Pulse until a crumbly dough is formed. Press the dough firmly into a greased 9-by-13-inch pan. Bake until just golden, about 13 minutes. Whisk together the condensed milk, egg, and vanilla. Pour the filling over the baked crust. Sprinkle the pecans, chocolate chips, and toffee pieces evenly over the filling. Bake until the filling is set, the edges are golden brown, and the toffee is melted, about 25 minutes. Cool completely in the refrigerator, about 2 hours. Cut into 32 bars.