1Preheat oven to 450 degrees F (230 degrees C). Scrub and dry potatoes, then prick several times with a fork and place onto a baking sheet.
2Bake in preheated oven until potatoes are easily pierced with a fork, 50 minutes to 1 hour. Remove and cool slightly. Cut potatoes in half lengthwise; scoop out pulp, leaving a thin shell.
3Reduce oven temperature to 350 degrees F (175 degrees C).
4Heat oil in a small saucepan over medium heat; cook and stir garlic until fragrant, about 2 minutes.
5Combine Alfredo sauce, garlic, pepper, and thyme in a small bowl. Stir in 3/4 cup Cheddar cheese, mozzarella cheese, and Parmesan cheese. Combine potato pulp and cheese mixture; mix well. Spoon mixture into potato shells; sprinkle with 1/4 cup Cheddar cheese.
6Bake in preheated oven until potatoes are hot and cheese is melted, about 15 minutes.
Footnotes
Tip
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.