The fastest way to collect 2 pies is on Level 1 and 2.
On Level 1, when the game prompts you to go right (right side of screen) or straight (left of screen) stay on the right side of the screen to enter a sort of free flight. After you enter the free flight you will want to keep your ship on the left side of the screen to head dead East. Eventually once you fly East enough you will see a pie start bouncing around the screen with MBG on it. Shooting it will produce score points, but make sure you actually maneuver your ship over it to pick it. After picking it up continue to finish the level.
On Level 2, do the exact same thing. Right side of screen for free flight, head dead East. Again you will see a pie bounce around the screen, the difference with this pie is that it will produce 1ups if shot, but again, make sure you actually pick up the pie. Continue to finish the level.
After completing Level 2 you will have also popped this achievement:
Doing this will also unlock the Ovoid ship so you can get this achievement: