Preheat oven to 350°F (175°C).

Line a 9 x 13 inch pan with aluminum foil and spray with cooking spray.

In a medium bowl, combine flour, hot chocolate powder, and salt.

In another medium bowl, beat butter and sugar with an electric mixer on high until light and fluffy (about 3 minutes).

Add egg and beat well.

Slowly add the flour mixture to the butter mixture and mix until just combined, scraping the sides of the bowl.

Spread the dough evenly in the prepared pan.

Bake until firm to the touch, about 30-35 minutes.

Transfer to a wire rack to cool for 5 minutes.

Lift the foil and cookies from the pan and place on a cutting board.

Slice in half lengthwise and cut each half crosswise into 3/4 inch pieces.

After the sticks have cooled, dot with vanilla frosting and let dry before storing.