Wash the potatoes thoroughly and cut larger ones into halves or quarters. Bring a large pot of water to a boil and cook the potatoes until slightly tender but not falling apart. Drain them well and set aside to cool slightly.
Thinly slice the onion and jalapeños. Crush the garlic cloves lightly to release more flavor into the brine. Keeping the vegetables evenly sliced helps them pickle consistently.
Heat olive oil in a skillet over medium heat. Add the onions and garlic and cook for a few minutes until softened and fragrant. This step enhances the overall flavor of the finished pickles.
Stir in the oregano, cumin seeds, peppercorns, and bay leaves. Let the spices toast briefly in the warm oil. This helps release their natural oils and intensifies their flavor.
Add the sliced jalapeños and cooked potatoes to the skillet. Pour in the vinegar, water, and salt. Stir everything together and bring the mixture to a gentle boil.
Carefully transfer the potatoes and vegetables into a clean glass jar. Pour the hot pickling liquid over the top until everything is fully submerged. Seal the jar loosely while it cools.
Once cooled, tighten the lid and refrigerate the jar. Allow the potatoes to sit overnight so the flavors fully develop. The taste becomes richer and more balanced after several hours.
Remove the potatoes from the refrigerator when ready to serve. Enjoy them cold, at room temperature, or alongside your favorite meals.