Combine basic mash ingredients in a sauce pan and bring to a boil. Simmer about 25 minutes till vegetables are tender.
While the basic mash vegetables are cooking, cut the leek into a fine length-wise julienne.
Bring the 1/4 cup of olive oil to high temperature in a cast iron skillet. Watch the oil carefully. I added the leeks once it started to spit to calm it down. Fry leeks over high heat until they start to turn golden brown. This took 4-5 minutes for me. Be careful not to burn them.
When the leeks start to turn golden remove them from the pan and drain immediately on a paper towel. Finish the leeks with good quality coarse sea salt such as Maldon.
When the basic mash vegetables are tender drain, reserving the cooking liquid.
Mash the basic mash ingredients, then add the Mash addition items stirring vigorously. If your mash is too dry you can add some of the reserved liquid til you get the consistency you want.
Transfer mash to serving or individual dishes depending on if you are plating the meal or not. Top with the frizzled leeks.