Mache, had never heard of it. Looked it up on Google. Lamb's Lettuce, Corn Salad.
Looks like it is something you would plant early Spring just like regular lettuce. I suppose you could start it indoors, but would not start it more than 6 weeks before it can go outside.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-