In a medium bowl, whisk together the all-purpose flour, cake flour, baking powder, baking soda, salt, and cornstarch.

In a stand mixer, beat the butter, granulated sugar, and brown sugar on medium speed for 2–3 minutes until light and fluffy.

Mix in the egg, egg yolk, and vanilla extract until smooth.

Gradually add the dry ingredients to the wet mixture while mixing on low speed until just combined.

Gently fold in both semi-sweet and milk chocolate chips along with chopped dark chocolate bar pieces.

Refrigerate the dough for at least one hour—or up to 24 hours.

Preheat your oven to 350°F (177°C).

Line a baking sheet with parchment paper.

Scoop large dough balls (about 1/3 cup each) onto your prepared sheet, leaving about three inches between each ball.

Bake for about 15–18 minutes or until edges are set but centers look slightly underbaked.