While it could be a lot of things, there are frequently three reasons that your Blondie bars may come out really greasy. u003cbr/u003eu003cbr/u003e1. You u003cstrongu003emay not have incorporated the butter, sugar, and/or eggs fully into your batter,u003c/strongu003e and therefore it wasn't blended enough to hold itself together properly.u003cbr/u003eu003cbr/u003e2. Your bars u003cstrongu003ecould definitely be underbaked. u003c/strongu003eYou could just extend the bake time, but firstu003cstrongu003e I would highly recommend getting an oven thermometer and checking that your oven temperature is actually where are you think it is,u003c/strongu003e and not running a little low. Your oven will also run below temp if you're frequently opening the door during the bake, so it's best to leave the door closed for as much of the bake as possible.u003cbr/u003eu003cbr/u003e3.u003cstrongu003e You just couldn't wait to cut them. u003c/strongu003eBecause these bars are so fudgy they really need time to set up out of the oven. Therefore, if you cut them 30 minutes after pulling them out, your bars may look really greasy, underbaked, and almost raw because the structure hasn't had time to solidify as it cools.