You mention you used to ride "a nice Bianchi trail bike". Do you
still have that bike? If so, why not ride it? Toss your stuff in
your daypack and off you go.

Two weeks before the end of Daylight Savings Time, start shopping for
a set of lights.

The most important thing is to find a bike that's comfortable.
Otherwise you won't want to ride. For a one mile commute, you can't
go terribly wrong with a Craigslist or garage sale bike. Don't worry
yet about racks and fenders and internally geared hubs and integrated
nav/comm systems - just get something cheap and in adequate condition
to get you into the habit of riding. You'll develop your own
preferences as you build experience.

My most recent commute (I work at home now) was 15 miles each way in
suburban sprawl traffic. I rode my skinny tire road bike with
panniers, and my trips were under 50 minutes. I mounted fenders and
lights in season. Over a period of years I have developed a
logistical system that worked for me. But you don't need all that to
get started - just toss your leg over a bike, and get started!