The filling for these pecan pie bars will remain slightly gooey when fully baked, but you'll want to make sure that the mixture isn't liquidy at the end of the bake time. Give the pan a jiggle -- it should move slightly in the center, but not slosh around. Under-baking will result in runny pecan pie bars. If the mixture isn't set at the end of the bake time, just continue to bake for 3-5 minute increments, then test again until it is set.