Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking pan.

Combine butter, powdered sugar, and salt in a mixing bowl; beat with an electric mixer until creamy. Gradually beat in flour. Spread dough into the prepared baking pan.

Bake in the preheated oven until light brown, about 15 minutes.

Combine sweetened condensed milk and chocolate chips in a microwave-safe bowl. Heat in the microwave for 1 minute. Beat until smooth.

Pour melted chocolate mixture over warm shortbread and spread evenly. Cool until set, about 30 minutes. Cut into small squares.