Line a 9x9 inch square baking tin with parchment paper, allowing the paper to overhang slightly on two sides for easy removal later. Preheat your oven to 160°C (320°F). This low temperature is crucial for brownies—it allows the chocolate and condensed milk to set gently without the edges becoming dry or overbaked.

Break the semi-sweet chocolate into small, uniform pieces and place them in a heatproof bowl or heavy-bottomed pan. Pour the sweetened condensed milk over the chocolate. Set the bowl over a pan of gently simmering water (double boiler method) or melt over low direct heat, stirring frequently until completely smooth and combined, about 3-5 minutes. I find the double boiler method gives you the best control and prevents the chocolate from burning—take your time here, as patience with chocolate melting makes all the difference in texture.

While the chocolate mixture is still warm, whisk together the flour, sea salt, and vanilla extract in a small bowl. Pour the dry ingredient mixture into the melted chocolate and condensed milk, folding gently with a spatula until just combined. Don't overmix—stop as soon as you don't see streaks of flour. I like to add the salt to enhance the sweetness and the vanilla to deepen the chocolate flavor; these small touches elevate a simple recipe significantly.

Pour the batter from Step 3 into the prepared tin, spreading it evenly into the corners with a spatula. Bake at 160°C for 20-25 minutes, until the edges are set but the center still has a slight jiggle when you gently shake the pan—the brownies will continue to cook slightly as they cool. The batter should look fudgy, not cake-like.

Remove the brownies from the oven and let them cool completely in the tin for at least 1 hour at room temperature. Once fully cooled, use the overhanging parchment paper to lift the brownies out of the tin and place them on a cutting board. Cut into squares using a sharp, dry knife, wiping the blade between cuts for clean edges. Serve at room temperature or chill before serving for a firmer texture.