Place the potatoes and the salt in a large pot. Add water to cover by 1 inch. Bring to a boil, then reduce the heat to a simmer. Simmer 15 minutes, until the potatoes are fork-tender. Drain the potatoes and transfer to a baking sheet, let cool slightly.
Use the bottom of a mug to smash each potato individually. Toss the potatoes with olive oil, onion powder, garlic, and season with salt and pepper, lightly breaking the potatoes as you toss. Transfer to the oven and roast the potatoes 30-35 minutes, tossing halfway through, until the potatoes are crisp and golden brown.
Meanwhile, make the vinaigrette. In a medium skillet, cook the chorizo until crispy. Drain off all but 1 tablespoon of chorizo grease. Let the skillet cool slightly, then add 2 tablespoons olive oil, the vinegar, fig tomato caramelized onion jam, and a pinch each of salt and pepper.
Toss the potatoes with the warm vinaigrette and serve with sour cream and freshly chopped chives.
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