Prepare the Pan: Place the mini chocolate chips in the freezer to chill. Line an 8×8-inch pan with parchment paper and set aside.
Heat-Treat the Flour: In a medium-sized bowl, measure out the all-purpose flour. Microwave the flour for 30 seconds to 1 minute, or until it reaches 165°F (74°C), to ensure it is safe for consumption. Stir and set aside.
Make the Cookie Dough: In a stand mixer or with an electric hand mixer, cream together the softened butter, granulated sugar, brown sugar, milk, and vanilla extract until thoroughly combined. Mix in the heat-treated flour and salt until completely incorporated. Set the cookie dough mixture aside.
Melt the White Chocolate: In a small microwave-safe bowl, combine the white chocolate chips and sweetened condensed milk. Microwave for 2 minutes, stirring every 30 seconds, until smooth and fully melted.
Combine Mixtures: Pour the melted white chocolate mixture into the bowl with the cookie dough. Stir until the mixture is smooth and well combined.
Add the Chocolate Chips: Quickly fold in the frozen mini chocolate chips to prevent them from melting.
Chill the Fudge: Pour the fudge mixture into the prepared pan and spread it evenly. Refrigerate for 2 hours or until firm.
Serve and Store: Once the fudge is set, cut it into squares. Store the fudge in the refrigerator until ready to serve.