I wonder...

Virginia Woolf said: As for my next book, I am going to hold myself from writing it till I have it impending in me: grown heavy in my mind like a ripe pear; pendant, gravid, asking to be cut or it will fall.

I wonder...Are you like Virginia? Do you let your stories simmer in your mind or do you start writing and figure it out along the way? Perhaps you do both depending on the story. I'd be interested to know what works for you and why. Please share.