Flour the lemon slices. Put the oil and lemon slices in a hot pan over medium heat and cook until the slices are caramelized and nicely browned on all sides. The flour will stick to the bottom of the pan a bit.
Add the garlic and capers and then deglaze the pan with the stock. Scrape the bottom of the pan to loosen any stuck flour bits. Reduce the sauce over medium heat until it has thickened a little and has a denser consistency. Add the butter at the end and season with salt and pepper to taste.