Spread flour on a baking sheet and bake at 350°F for 5 minutes to heat-treat. Let cool completely.

Melt butter and brown sugar in a saucepan over medium heat, stirring until smooth.

Stir in sweetened condensed milk. Bring to a gentle boil and cook for 2 minutes, stirring constantly.

Remove from heat. Stir in vanilla, salt, and heat-treated flour until well combined.

Fold in mini chocolate chips.

Press mixture into a parchment-lined 8x8 inch pan. Refrigerate for at least 2 hours until firm.

Cut into squares and serve. Store in the refrigerator.