Apple cores do not have to be hand pieced. I am now working on a scrappy one. I admit I have the GO die and it has the little triangle at the center of each curve to help guiding that seam......two pins/ first at center- finger folded, then second are the beginning, making sure the edges are straight. Set under needle, lower needle to hold that edge, remove pin, and go SLOW...oops forgot - smile on the bottom, frown on top(at least that works for me). Watch just in front of foot, guide by moving right hand to left ( bottom fab) and left hand(top fab) to right.....after matching and sewing that center point and as you approach the end, hold those two ends together with a tweezer.....easy peasy.....
I find doing rows is the easiest way to construct...but that's just me