When baking a cake you should always line the bottom of the pan with parchment paper, prior to greasing and flouring. Here’s an easy way to make a custom-fit parchment circle:
Tear a sheet of parchment paper that is slightly larger than the pan. Fold it in half, from bottom to top.
Fold in half again, this time from right to left.
Fold the top right corner down to meet the bottom left corner.
Fold the top edge down to meet the bottom.
Turn your baking pan upside down and place the folded “point” into the center.
Make a cut just inside the edge of the pan; continue cutting in a slight curve.
Open the paper up – you should have a circle that fits perfectly in the bottom of your pan.
Of course, you can always buy pre-cut parchment circles. But you might need a circle that’s a different size, in which case you’ll find that this technique comes in handy!