Place chopped potatoes into a pot and fill with water. Place over high heat and boil until potato is fork tender. Drain into a colander, then place potatoes back into pot.
Place butter in a small saucepan and melt over medium heat. Continue to cook until butter bits at the bottom of the pan have browned and omit a nutty aroma. Remove from heat and pour over potatoes, scraping out as much of the browned bits as possible.
Season potatoes with a generous amount of salt and pepper and mash with a potato masher. While potatoes are still lumpy add cream and continue to mash until smooth.
Adjust seasonings as needed. Cover and set aside.
Place a large skillet over high heat. Generously season steak with salt and pepper.
Melt butter and oil into skillet. Add garlic clove and thyme and cook for about 1 minute.
Add steak to skillet and sear on each side for about 3 minutes.
Lower heat to medium-high and slightly tilt skillet so butter and oil pile into bottom. For the next 2 to 3 minutes, spoon hot, melted butter and oil mixture over steak, fully basting entire steak. Remove from oven and transfer to a cutting board.
To serve: Pile mashed potatoes onto a platter and top with steak. Spoon some of the basting mixture over steak and serve.