Preheat the oven

• Preheat the oven to 175 °C.

Brown the butter

• Melt the butter in a saucepan over medium heat.
• Once boiling, swirl the pan or stir constantly until the butter turns a deep amber color.

Mix the dry ingredients

• Whisk together the flour, baking soda and salt in a bowl.
• Set aside.

Combine the wet ingredients

• In a separate bowl, combine the cooled brown butter, oil, brown sugar and granulated sugar.
• Whisk until a smooth paste forms.
• Crack in the egg and add the vanilla extract, then mix until well combined and smooth.

Make the batter

• Add the dry ingredients to the wet batter and gently fold until just combined.
• Add the chocolate and mix with a spatula until evenly distributed, avoiding overmixing.

Assemble and bake

• Line an 8x8-inch baking pan with parchment paper.
• Press the batter into the prepared pan.
• Bake until lightly golden.

Finish and cool

• Remove from the oven and sprinkle with flaky sea salt.
• Allow to cool completely in the pan before serving.