Measure 20cm from one end of an aluminum strip and mark a line across it. Measure 20cm in from the opposite end and mark it again. This will divide your strip into three sections: 20cm, 30cm and 20cm. Repeat the process with a second strip.
Lay the strip on a workbench and place the circular dowel over the first mark you have made. Press down firmly on the dowel and grip the longer end of the strip with the pliers. Bend it upward until you have created an L-shaped strip with a 90-degree bend in it. Repeat the process with the other strip.
Move the dowel to the second mark, press down firmly, and bend the strip up to 90 degrees and just beyond. This will leave you with a "C-Shaped" piece, where the top horizontal section slopes downward slightly. This will form the shelf where your laptop will sit. Repeat the process with the other strip.
Slide the bottom portion of the strip underneath your mixer to check the dimensions. The vertical section of the strip should adequately clear your mixer. Once satisfied, drill a hole in each strip, and at either end of the 30cm strip. Attach it to the "C-shaped" sections using the wingnuts. This will add stability and allow you to disassemble the stand for transport without the need for tools.
Glue the strips of rubber matting onto the top surface of the stand, where the laptop will sit, and then place it on there to check the grip is adequate. If not, try reducing the angle of slope.