Mix together the sugar, egg white and cream of tartar to create the "mortar."
Assemble sugar cubes into a 10-cube x 10-cube square at the center of the cardboard. Use the pastry brush to brush the "mortar" mixture in between each cube as you create the square. If you want to create a larger pyramid, simply increase the number of cubes evenly on each side of your square.
Center a nine-cube by nine-cube square on top of the first square. Each side will be approximately 3cm in from the sides of the bottom square. Apply the mortar to both the bottom and sides of the cubes as you create the second layer.
Repeat step three, but this time make the square eight cubes x eight cubes. Continue making the squares progressively smaller until the pyramid is complete. Top the pyramid with one cube at the highest point.
Paint the pyramid in tan or yellow and let dry. For the look of sand sparkling in the sun, you can sprinkle gold glitter over the pyramid while the paint is still wet.