It is sarsa time in Madison. The hot August sun has ripened the tomatoes, and Monona Bay that skirts 'Little Italy' seems congealed in silver silence. It is the season before the gnat invasion.~from Old World Wisconsin by Fred L. Holmes, published in 1944. Other nationalities are at the "Old World Wisconsin" tag.
All along lower Regent Street, in adjoining backyards and open spaces off Milton Street, Italian housewives are vigilantly guarding the sarsa boards from the threat of rain. Within the homes the kettles are boiling—big kettles filled with sliced red tomatoes. When after an hour the cooking has turned the bubbling pulp into a thin red sauce, the contents are strained. Then the squishy mass is poured on clean white sarsa boards and placed in the sun to evaporate. Every hour, or oftener, the thickening nucleus is spread and respread until it takes on a richer shade and becomes a heavy relish. As it is packed away in jars, olive oil is poured on top—enough to form an air-proof covering. The finished product is then ready for use—all fall, all winter, all spring—until another crop of red tomatoes can be harvested.
"Sarsa" is Sicilian dialect for salsa.
Here's a link to a photo of a woman preparing "sarsa" in Madison. link
I especially like the simple trick of pouring oil over the sarsa to keep out air. That's exactly how commercial sodium and potassium metals (both air and moisture sensitive) are sold--submerged in oil to protect them.