It cooks them one at a time, although you only need to click once. It's still better cooking exp than using a range because you can't burn the pies and you can do it in a bank, but the process of gathering ingredients for pies (and putting them together) takes so long that the exp is less efficient than, say, cooking lobsters. I hadn't thought of the pot sharing technique, but I strongly suspect that Jagex is going to nerf it. it cooks all pies at once, doesn't it? the phrase they used was any, but i assume they mean all.