If you hesitate and pull the pan early, thinking they will continue to cook some after removal from oven (they will but not much, not enough sometimes), then let them cool the recommended “fully cooled” of many recipes. And still find the toothpick wet after checking or the knife cuts it more like a pudding.

You can still reheat the oven and bake them checking every ten or five minutes. You may even notice the center finally puffing up as it finally cooks through.

They might even burn around the edges.

But, don’t think you can’t do this fully reheat baking in order to firm up the whole thing.

The bigger worry of burning the whole thing, because from that you cannot recover. As long as you do check the second bake every five to ten minutes, you should find only the already baked edges might burn.

Why have I said all of this (even repeating myself)?

Don’t throw out and especially don’t eat the under baked pan of brownies. They deserve a second bake even if you let them fully cool overnight (thinking some magical baking aspect with let the gooey mess set properly).