Align the two apples so they're off center to one another. One has 2/3 on the outside to the left, 1/3 to the right, the other 2/3 to the outside to the right, 1/3 to the left.

Bird's eye view, the single line cutting both apples will leave us with the left 2/3 of the first apple and the right 2/3 of the second, and a third portions made of 2 thirds, or another 2/3 of an apple.

One cut, 2 apples, 3 equal portions.