In a large bowl, cream butter and cream cheese until light and fluffy. Gradually add sugar and beat until smooth. Add egg and vanilla, mixing well.
In a separate bowl, whisk flour, cornstarch, and pumpkin spice. Gradually add to butter mixture until combined. Divide dough in half and chill for 1 hour.
Roll dough to 1/8-inch thickness on parchment paper. Use circular and wedge-shaped cutters to create pie slice shapes. Chilled dough again for 30 minutes.
Bake at 350°F (175°C) for 12-14 minutes until just golden. Cool completely on wire racks.
Make royal icing by blending powdered sugar, maple syrup, and water to a thick flood consistency. Add gel food coloring if desired. Pipe pie slice designs onto cooled cookies.