Heat oil in large deep pan over medium high heat until smoking. Add garlic and cook at steady sizzle, tipping pan occasionally to cover garlic in oil, until golden brown spots appear and skins begin to split and blister, about 5 minutes.
Shove garlic to the side of pan, put rosemary into the oil next to garlic. Spread peanuts into remaining space in pan. Reduce heat to medium, let rosemary sizzle a minute before stirring everything together.
Cook, stirring occasionally, about 4 minutes. Season with salt and crumble the chilies into the pot; cook another minute. Remove pan from heat, but let peanuts cool in pan a bit. Adjust seasoning as needed.