Let the butter soften at room temperature.

Whip the butter until creamy using a whisk or hand mixer.

Gradually add sugar and salt in three portions while whipping until fully dissolved.

Add eggs one at a time and whip quickly to prevent separation.

Prepare the dark couverture chocolate.

Melt the chocolate using a double boiler method.

Add the melted chocolate to the batter.

Sift cake flour, cocoa powder, and baking powder into the batter.

Fold the dry ingredients into the batter using a cross-cutting motion.

Add milk and mix until the batter is smooth.

Transfer the batter into a piping bag.

Line muffin tins with parchment paper and fill each tin 2/3 full with batter.

Optionally sprinkle chocolate chips on top.