Bar Tartine is not so much a restaurant as it is a laboratory.

Having created an innovative dinner menu, chef Nicolaus Balla and pastry chef Cortney Burns are now taking on the midday meal with rare enthusiasm.

A lentil croquette sandwich ($12) is reminiscent of falafel, the fried orbs smashed on a slab of whole-grain bread baked that morning by co-owner Chad Robertson. The croquettes are joined by charred Padrón peppers, lavished with house-made yogurt and topped with sprouting grains.

In Balla and Burns' larder, all manner of ingredients are drying, fermenting and curing. The sunflower seed-and-white bean dip ($11), accompanied by cucumber slices and peeled heirloom cherry tomatoes, is garnished with briny house-cured olives, and dusted with Balla's version of shichimi togarashi; his version includes dried kale, nori and house-dried chiles.

The smørrebrød ($6 each; three for $15), previously available only at brunch, are built on slices of Robertson's sturdy rye bread. Our favorite was the blue cheese, bacon, egg and avocado. The cheese is transformed into a silky spread, the egg has an oozing yolk, and the bacon is a crisp flag.

In this lab, we happily submit to experiments.

Bar Tartine, 561 Valencia St. (at 17th St.); 415-487-1600 or bartartine.com