Preheat the oven to 140°C (285°F). Low-and-slow roasting concentrates tomato flavor and gently caramelizes the sugars without burning — higher temperatures will cause the garlic to scorch and the tomatoes to split too harshly.

Core and halve the tomatoes lengthwise. If very large, quarter them. Halving exposes the flesh so they roast evenly and the liquid reduces into a jammy texture. Place the cut tomatoes cut-side up in a single layer in a shallow baking dish.

Scatter the diced onion and sliced garlic evenly over and between the tomatoes. Onions add sweet backbone when slowly caramelized; sliced garlic becomes soft and mellow rather than sharp when roasted.

Sprinkle the granulated sugar evenly over the tomatoes and onions. The sugar accelerates caramelization and amplifies natural tomato sweetness, producing a glossy, concentrated finish.

Drizzle the olive oil over everything and sprinkle the dried oregano, thyme, kosher salt and black pepper. The oil helps conduct heat and mouthfeel, while the dried herbs give classic Mediterranean aromatics that hold up to long roasting.

Roast uncovered in the preheated oven for 75–90 minutes, rotating the dish once after 40 minutes for even browning. Roast until tomatoes are deeply colored, edges caramelized, and most of the liquid has reduced to a thick, jam-like consistency. The long roast both concentrates acids and softens the tomato flesh into a silky texture.

While the tomatoes roast, brown the butter: place the butter in a small saucepan over medium heat. Swirl occasionally until the milk solids turn golden-brown and the butter smells nutty (about 4–6 minutes). Browning the butter adds a toasty, savory note that contrasts the tomatoes' sweetness.

Remove the roasting dish from the oven when jammy. Use a wooden spoon to gently press any larger tomato pieces against the side of the dish to release and integrate their flesh — but leave some intact pieces for texture. Taste and adjust seasoning (you may want a pinch more salt to balance the sweetness).

Stir about half of the browned butter into the hot tomatoes to enrich the confit and give a silky sheen. Reserve the remaining browned butter for finishing individual portions or toasting bread. The hot fat melds flavors and adds mouth-coating richness.

Let the confit cool slightly (10–15 minutes). Serve warm or at room temperature. Use as a spread on grilled bread, a condiment for roasted chicken or fish, or spooned over creamy polenta. The concentrated tomatoes will taste both sweet and deeply savory — the finished dish should be glossy, jammy and aromatic.

Store leftovers in an airtight jar in the refrigerator for up to 7 days — the flavor improves after a day as the aromatics marry. Reheat gently in a skillet, adding a splash of water if the mixture is too thick.