There's an airfield on the Eastern shore of Silver Lake; look for an old plane propped on top of a pole. One of your junkyards is near this location too.
At the airfield are a bunch of ramps. The one we are looking for in particular goes up and through a hangar and is right near a super-jump that goes through a big ring hanging from a crane; it's marked with glowing blue traffic cones.
Line up your car so you have a good long straight run at the ramp. Hit the gas, and hold down A
to kick in the nitrous.
As you're going up the ramp, stay on the right side: There's another smaller split ramp at the end of the main jump. Make sure your right wheels go up the split ramp, and hold the left analog stick to the left to cause your car to go into a barrel roll. Do it correctly, and you should be able to do at least three barrel rolls and have plenty of time to land properly.
Use your best stunt car for this jump; I used the Carson GT Concept