You can earn this Trophy by simply replaying the first race (Grass Hills) in the San Francisco area of the California cup with any car that you've unlocked. As long as you come in first place 20 times in a row, regardless of what race or car you choose, you'll meet the Trophy requirement. Also, if you're having trouble winning, you can perform a Boost Start by holding down R2 to fill the gauge in the upper right corner. You need to start pressing R2 after the timer reaches 1 and the gauge has to be half full, otherwise your car will not boost when the race begins.