Rinse the salmon under water and pat dry with paper towels. Season with salt and pepper.
Heat a skillet (cast iron preferred) over medium heat. Add the butter and let it melt before adding the salmon, skin side down. Add the garlic and thyme.
Pan-sear the salmon, uninterrupted, for about 1 minute. Flip the salmon and sear the other side for another minute, turning the garlic as well to prevent burning. Spoon the melted butter over the salmon while it cooks.
Flip the salmon back to skin side down and sprinkle cayenne pepper on top. Add a squirt of fresh lemon juice and a pinch of salt to taste. Turn off the heat and serve immediately.