In a 9-inch baking dish, line with wax paper and set aside.
In the bowl of a food processor, add peanuts and crackers pulse until barely combined. Add sugar and process for 10 seconds before pouring in sweetened condensed milk; process until dough is formed. If wanted, add salt during the process.
Transfer the mixture to the prepared baking dish and compact it with clean hands. Then use a small measuring cup to smooth and level it out. Cover and transfer to the fridge for at least 4 hours or overnight.
Remove from the dish by lifting with the wax paper and cut into squares. Place squares in an airtight container.