What Is This Yellow Stuff Growing On My Deck?

When I got up this morning to let the dogs out (what? It was me this whole time?), I noticed this stuff growing on my deck:

The searches I tried include: fungus, deck plant, what is this stuff growing on my deck, yellow flowery thingy, have aliens claimed my deck as their new territory - none of them brought up a satisfactory answer.

Do you know what this stuff is? (Follow-up question: can I cook it?)