Place a chopstick (or wooden skewer) on each side of a potato to create a physical block for your knife. This helps prevent you from cutting through the potato, so you can create the "accordion effect."
Using a sharp knife, place deep cuts in the potato every 1/4", stopping when your blade hits the chopsticks (or skewer).
Repeat this process for all of your potatoes.
Once you're done cutting them, place the potatoes on a parchment paper lined cookie sheet.
Melt half of the butter and olive oil in a saucepan with the smashed garlic cloves and thyme.
Pour over the potatoes, ensuring ensuring it gets into as many of the slices as possible.
Bake the potatoes for 50-60 minutes, until golden and crispy. Melt the remaining butter and olive oil with the garlic and thyme. Brush the melted butter-oil mixture on top of the crispy potatoes. Season with salt and pepper and garnish.