Preheat the oven to 375 degrees F.
Heat a skillet over low heat and add 1 tablespoon of olive oil and butter. Add the shallots with 1/4 teaspoon salt and stir to coat. Cook the shallots, stirring every few minutes, until the slightly golden and caramely, about 15 minutes. Stir in the brown sugar and cook for another 10 minutes. If at any time, the shallots seem to be burning or crisping up, reduce the heat.
While the shallots are caramelizing, toss the tomatoes with the remaining tablespoon of olive oil, 1/4 teaspoon of salt and pepper. Stick them in the oven and roast for 15 to 20 minutes, until they just begin to burst.
Combine the tomatoes, shallots and cilantro in a bowl. Mix and mash it together with a fork. Taste and season additionally with salt and pepper if needed.