In a food processor, pulse together the peanuts, sugar, flour and salt until coarse. Pour in the sweetened condensed milk and pulse again, stopping to scrape down the sides when needed. The dough will be slightly sticky.
Shape into balls, cylinders or squares and set on parchment lined baking sheets to firm up. It takes about 20 minutes to firm. No baking necessary.
Store in an airtight container at room temperature for up to one week.