I can't find a thread dedicated to this amazing bakery, so here it is - I've been twice recently - the baguette, pain au levain, and multigrain loaf (basically the levain with seeds crusted on the outside) are all outstanding - right up there with B&R, Clear Four, and Iggy's IMHO.
It's small, they only have basic breads and are open Tues-Sun 9a-3p on a side street in Winchester (across from Swanton St Diner and close to Rt 38 Main St between Winchester Center and Woburn). Also not far from the magnificent dessert muffin (aka cupcake) shop Gingerbread Construction Company.
Mamadou's is worth a detour if you want GREAT bread. Other threads note they are at the Arlington Farmer's Market (and others?) in season, and Parsons Table serves the bread - more places should also.
Mamadou's Artisan Bakery
63 Swanton St, Winchester, MA 01890