Bring a large pot of water to a rolling boil over high heat. While waiting for the water to boil, use a paring knife to score a small "X" on the bottom of each tomato.
Prepare an ice bath by filling a large bowl with equal parts ice and cold water. Carefully lower the scored tomatoes into the boiling water and blanch for 60-90 seconds, until the skins just begin to peel back at the "X."
Immediately transfer the blanched tomatoes from the pot to the ice bath using a slotted spoon. Let them sit for 1-2 minutes to stop the cooking process, which will make the skins very easy to remove.
Peel the tomatoes by gently pulling the loosened skins away starting from the "X." Core the tomatoes by cutting out the tough stem end, then cut them in half crosswise and gently squeeze out the seeds into a bowl to discard.
Transfer the peeled, cored, and seeded tomato halves to a large, clean bowl. Use your hands or a potato masher to crush the tomatoes until they reach your desired consistency, from chunky to more broken down.
Heat the olive oil in a large, heavy-bottomed pot or Dutch oven over medium heat. Add the crushed tomatoes, kosher salt, and sugar, stirring to combine. Bring the mixture to a gentle simmer.
Reduce the heat to low and let the tomatoes simmer, uncovered, for 30-45 minutes, stirring occasionally. Cook until the raw tomato taste has mellowed and the sauce has thickened slightly to your liking.
Taste and adjust seasoning with more salt if needed. Use immediately, or let cool completely before storing in airtight containers in the refrigerator.