In a heavy-bottomed skillet, melt the butter over medium heat. Once melted, allow it to foam and cook until small brown flecks form at the bottom and the butter gives off a nutty aroma. Immediately transfer to a heatproof bowl to prevent burning. Refrigerate until softened, approximately 30 minutes. If overchilled, allow it to rest at room temperature until spreadable.

Preheat the oven to 350°F (175°C). Lightly grease a 9x5-inch loaf pan with cooking spray or butter, then line with parchment paper, allowing the edges to overhang for easy removal.

In a medium bowl, sift together the flour, cornstarch, baking powder, and salt. Whisk lightly to ensure even distribution and set aside.

In a stand mixer fitted with the paddle attachment or with a handheld mixer, beat the softened butter and brown sugar on medium-high speed until pale and creamy, about 2 minutes.

Scrape down the sides of the bowl with a rubber spatula. Add the eggs, one at a time, mixing well after each addition. Blend in the vanilla extract until the mixture is fully combined. The batter may appear slightly curdled at this stage; this is normal.

Reduce the mixer speed to low. Add one-third of the flour mixture, followed by 2 tbsp of milk. Repeat the process, alternating between flour and milk additions, finishing with the final portion of flour. Mix until no visible streaks of dry ingredients remain. Use a rubber spatula to give the batter a final stir, ensuring all ingredients are well incorporated.

Pour the batter into the prepared pan and smooth the top with a spatula. Bake for 40–45 minutes, or until a toothpick inserted into the center comes out clean. The cake should be golden brown with a slightly domed top.

Allow the cake to cool in the pan for 15 minutes, then carefully lift it out using the parchment overhang. Transfer to a wire rack to cool completely. Slice and serve at room temperature or slightly warm.