Bring water to a boil in a large pot. Add potatoes, garlic and salt and cook on medium heat until potatoes are fork tender, about 15 minutes. Turn off the heat.
Drain potatoes and garlic, reserving 1 cup of cooking liquid. Using a potato masher, fork or beater, combine the potatoes, garlic, olive oil and thyme in the large pot. Add as much of the reserved cooking liquid to reach desired consistency.
Transfer to a serving bowl, and serve warm with a drizzle of olive oil, fresh thyme and freshly cracked black pepper, if desired.
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Notes
Storage: Store any leftover mashed potatoes in an airtight container in the fridge for up to 5 days. Make Ahead Instructions: Let them cool to room temperature before storing in a container in the fridge. They will keep well for 3 to 4 days. Reheat the potatoes gently on the stovetop, stirring in some extra olive oil and the cooking water so that they don't stick. You can also stir in some vegetable broth while you reheat.