Place the chocolate chips in the freezer. Then, start by heat-treating the flour to kill any bacteria. Add the flour to a microwave-safe bowl and microwave in 30-second increments, stirring in between each (about 2-3 minutes), until the flour reaches 165℉ on a thermometer. Cool completely.
1 ⅔ cup all-purpose flour
Cream together the butter and sugars on medium-high speed for about three minutes until fluffy. Add the vanilla, peanut butter, and salt and mix to combine, then scrape down the sides.
½ cup unsalted butter, ½ cup light brown sugar, ¼ cup granulated sugar, 1 teaspoon vanilla paste or extract, ⅓ cup creamy peanut butter, ¼ teaspoon kosher salt
Sift the flour into the mixture (leaving any hard clumps behind) then mix on low speed. Once all flour has been incorporated, add in the sweetened condensed milk in a steady stream with the mixer running on low.
14oz can sweetened condensed milk
Scrape down the sides once more, then add the cold chocolate chips and mix on the lowest setting until evenly dispersed.
1 cup mini semi-sweet chocolate chips
Prepare an 8x8-inch baking pan with parchment paper slings, then add the dough to the pan. Using a spatula, bottom of a measuring cup, or clean fingers, press the dough evenly across the pan, being sure to get the dough the whole way into the sides and corners.
Place in the fridge to set for about 30 minutes.
To make the topping, add the peanut butter and chocolate to a bowl and microwave in 20-second increments, stirring after every 20 seconds, until completely smooth. You could also do this in a double boiler. Pour over the chilled cookie dough and spread evenly.
½ cup creamy peanut butter, ½ cup chocolate chips or chopped chocolate of any variety
Allow it to sit for 5 minutes, then sprinkle with flaky sea salt. Return to the fridge for another 30 miuntes.
Once chilled, slice into the desired number of pieces (up to 36), and serve.