Prepare the oven and baking pan. Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving a slight overhang on the sides. This ensures easy removal and helps prevent the brownies from sticking or breaking.

Melt the chocolate and butter. Add the chopped dark chocolate and butter to a heatproof bowl. Melt gently over a double boiler or in the microwave using 20–30 second intervals, stirring between each round. Stop as soon as the mixture is smooth and glossy to avoid

Add condensed milk and eggs. While the chocolate mixture is still warm, stir in the sweetened condensed milk until fully combined and creamy. Add the eggs one at a time, mixing thoroughly after each addition to maintain a smooth, stable batter. Stir in the vanilla extract if using.

Incorporate dry ingredients and fill the pan. Sprinkle the flour and salt evenly over the batter. Gently fold with a spatula just until the flour disappears—do not overmix. Pour the batter into the prepared pan and spread it evenly, smoothing the surface for uniform baking.

Bake, cool, and slice. Bake for 22–28 minutes, until the edges are set and the center remains slightly soft. A toothpick inserted should come out with moist crumbs. Allow the brownies to cool completely in the pan before lifting them out and slicing for clean, fudgy pieces.