Instructions

• Sift the cake flour, bread flour, baking soda, baking powder, and kosher salt into a medium bowl and set aside.
• Fit a mixer with the paddle attachment. Add the cooled browned unsalted butter, packed light brown sugar, and granulated sugar to the mixer. Beat at medium speed for about 3 minutes, until smooth and combined.
• With the mixer running at medium-low, add the 2 large eggs one at a time, mixing well after each addition. Add the egg yolk and mix until incorporated. Stir in the vanilla extract.
• Reduce the mixer speed to low. Add the sifted dry ingredients and mix only until just combined, about 5–10 seconds. Scrape the bowl as needed.
• With the mixer still on low, gradually add the dark chocolate chips and the Heath toffee bits. Mix only until they are evenly distributed and the dough is just combined. Do not overmix.
• Press plastic wrap directly against the surface of the dough to prevent a skin from forming. Refrigerate the dough for 24 to 36 hours. (The dough can be used in batches and may be refrigerated for up to 72 hours total.)
• When ready to bake, remove the dough from the refrigerator and let it sit at room temperature for about 30 to 60 minutes to soften slightly. While the dough is softening, preheat the oven to 350°F and line a baking sheet with parchment paper.
• Portion the dough into balls about 3 ounces each using a scale or cookie scoop.
• Place the dough balls on the prepared baking sheet, leaving a few inches between each to allow for spreading.
• Bake at 350°F for 16–18 minutes, until the edges are golden brown but the centers still look soft.
• If desired, immediately sprinkle the hot cookies with flaky sea salt right after they come out of the oven.
• Transfer the baking sheet to a wire rack and let the cookies rest on the sheet for 10 minutes, then move the cookies to another wire rack to finish cooling. Repeat with remaining dough, or keep leftover dough refrigerated for baking later.