Throw the flour into the loaf pan. Smooth-out the lumps with a butter knife. Pour in the oil and stir with a small whisk. Set the microwave for 15 minutes and cook control to 60%. Start the microwave. At one minute intervals, stop, whisk the roux and restart the microwave - until the roux becomes the color of light chocolate. From this point on, stop, whisk the roux and restart the microwave at 30 second intervals - until the roux becomes dark chocolate brown. Remove the roux from the oven and stir - periodically - until cool. The residual heat should turn the roux to a brick color.
The above, microwave method of roux-making requires 12-13 minutes to achieve a dark (chocolate) roux.