Caffé Umbra, a simply decorated restaurant serving rustic French (and some Italian) fare, is the product of chef/owner Laura Brennan’s 20-year love affair with food. It’s lucky for her patrons the romance has only deepened over time. She not only pulls together interesting combinations of foods, like green apple and melted leek gratin or prune mustard with pancetta, along with old-style French entrées, but she delivers dishes that burst with complex, rich flavors. Everything on the menu, which changes often depending on what is fresh and available, is cooked to order, slowly and carefully, our waitress reported. Yet another feat, considering the relentless demands on a restaurant owner who also (wo)mans the kitchen.

The inviting bar of polished cherry wood offers an array of unusual specialty drinks (and a well-chosen wine and beer list), so we started with a mango daiquiri, shaken, not frozen. French rolls arrived with butter, which Brennan prefers to olive oil. Seated in front of large windows, we had an impressive view of the magnificent, gothic Cathedral of the Holy Cross, right across the street, which is illuminated at night, casting a mystical glow. (Umbra, the blackest part of a shadow, alludes to the restaurant’s location vis-à-vis the church.)

The Blue Hill Bay mussels ($12), dripping with a white wine and herb broth, were the most flavorful and tender I’ve tasted. The appetizer was accompanied by mustard aioli and pencil-thin French fries, perfectly crunchy and salted. The roasted beets (and cauliflower, it turned out) with Gorgonzola fonduta ($9) was a delicious pairing. (Don’t expect a viscous, heart-stopping "cheese fondue" experience; fonduta is more a liquid sauce.) A toothsome salmon entrée ($21) came with sweet dots of currants in a brown sauce which together formed a nice complement to the savory fish. Sunchoke purée added an unusual twist. A classic French cassoulet ($21) arrived with aromatic steam rising from the plate. The tarbais beans (small white beans, hand-picked in France, that hold their shape and flavor in slow-cooked casseroles) offered gentle neutrality against the saltier, gamey essence of the duck-leg confit and house-made lamb sausages. The dish was absolutely exceptional. Also available are side orders of choice vegetables, onion rings, and eggplant frites ($4.50). The last had an elaborate coating and very little eggplant taste, but was good anyway, especially dipped in a plum sauce.

Pastry chef Ron Roy produces a signature dessert: sticky toffee pudding with a warm toffee sauce and vanilla ice cream ($9). More dense, gooey cake than jiggling pudding, this incredible creation could not have been sweeter, with its satisfying, burnt-sugar sizzle. Also good was the apple-pear pie ($6): a soft crust covered a blended fruit filling flavored with amaretto. We could not resist trying one of the homemade ice creams: a dainty scoop of the chestnut ($3) tasted of sweet smokiness.

Caffé Umbra’s plain setting, with mustard-yellow walls and natural wood, offers a solid frame within which diners can focus on what Brennan does best: cook terrific food.