Alien plant

I've brought most of the last green tomatoes inside to ripen on the kitchen windowsill which gets the afternoon sun. Tonight's dish was chicken kiev with simple tomato rice using cherry tomatoes from the garden. Simple but delish.

Something I'm far less inclined to taste is this strange looking growth I found the other day. The stalk was quite thick and mushroom like, the flower part about the size of my palm. It's dried out considerably since then so I'm thinking it was the result of frequent rain recently. Anyone know what it is?