Line an 8×8” (20x20cm) square pan with parchment paper or aluminum foil. If using aluminum foil, lightly butter the surface to prevent sticking. Set aside. Measure out your chocolate chips at this point, too, dividing them into ½ cup (85g) and ¼ cup (40g) measurements.

Heat-treat flour by placing in a microwave-safe dish and heat in 10-second increments until it reaches a temperature above 160F (71C). Set aside.
1 cup (125 g) all-purpose flour

In a medium-sized saucepan, combine white chocolate chips, condensed milk, butter, sugar, and salt. Turn stovetop heat to medium low and stir frequently until butter and chocolate chips are completely melted and mixture is smooth.

2 cups (340 g) white chocolate chips,14 oz (396 g) can sweetened condensed milk,6 Tablespoons (85 g) unsalted butter,½ cup (100 g) light or dark brown sugar,¾ teaspoons table salt

Reduce heat to low and sift flour into the pan, then stir until completely combined.

Remove from heat, add vanilla extract, and stir well.
2 teaspoons vanilla extract

Working quickly, add ½ cup (85g) chocolate chips and stir until *just* combined (don’t overmix or your cookie dough fudge will become very chocolatey!). Immediately pour into prepared baking pan and smooth with a spatula if needed. Sprinkle remaining chocolate chips evenly over the surface.
¾ cup (125 g) semisweet chocolate chips

Allow fudge to set completely at room temperature, this usually takes 2-4 hours, then slice and serve!