This French Technique Is the Key to the Most Flavorful Mashed Potatoes Ever

Meanwhile, cut 8 tablespoons unsalted butter into 8 pieces and refrigerate until ready to use. Transfer all but 2 tablespoons of the garlic oil to a bowl or airtight container and reserve for another use. Add the mashed garlic, 3/4 cup whole milk, and 1/3 cup heavy cream to the saucepan. Bring to a simmer and cook until the mixture is just warmed through but not boiling, about 5 minutes.