Heat 2 tablespoons of the oil and 1 tablespoon of the butter in a medium saucepan over medium-high. Add leeks and garlic; cook, stirring often, until tender, 5 to 7 minutes. Stir in rice and thyme; cook, stirring until coated, 1 to 2 minutes. Add wine; cook, stirring constantly, until absorbed, about 1 minute. Add 2 cups of the warm stock and 1 teaspoon of the salt to rice mixture. Cook, stirring often, with a wooden spoon or rubber spatula, until almost absorbed, about 10 minutes. Continue adding remaining warm stock, about 1 cup at a time, stirring constantly until most of the liquid has absorbed between additions, about 25 minutes total. Rice should be tender and saucy. Remove and discard thyme.