Sift together the flour, cocoa powder, cornstarch, baking soda, salt, and cinnamon in a medium bowl. Sifting is essential here—it removes lumps from the cocoa powder and ensures even distribution of the leavening agents, which gives you a more tender, evenly-colored cookie. Set this mixture aside and preheat your oven to 375°F while you prepare the wet ingredients.

In a large bowl, beat together the butter, shortening, and sugar for about 4 minutes until the mixture is light, fluffy, and pale in color. This creaming process incorporates air into the dough, creating a tender crumb and helping the cookies spread evenly. Use an electric mixer on medium speed to ensure you're aerating properly throughout.

Add the room-temperature egg, egg yolk, vinegar, vanilla, and red food coloring to the creamed mixture. Beat until fully combined and the dough has a vibrant red color. The room-temperature egg incorporates more smoothly and evenly distributes the color. I use liquid food coloring for easier mixing, though gel works too—just dissolve it in the vinegar first for even distribution.

Add the dry ingredient mixture from Step 1 to the wet ingredients and mix on low speed until just combined—don't overmix or the cookies will be tough. Fold in the 3/4 cup white chocolate chips by hand using a spatula or wooden spoon. The contrast of the creamy white chocolate against the deep red dough creates both visual appeal and flavor complexity.

Roll about 1.5 tablespoons of dough into balls and place them about 2 inches apart on ungreased baking sheets. Press 6 chocolate candies into the top of each ball, gently pushing them down so they stick. This is a great time to let someone help—kids especially love pressing the candies in! The candies will soften slightly during baking and create little pockets of chocolate flavor.

Bake for 8-9 minutes until the edges are set but the centers still look slightly underdone—this is key to keeping them soft and cake-like. The cookies will continue cooking on the hot pan, so don't overbake. Let them cool on the baking sheet for 2-3 minutes, then transfer to a wire cooling rack to finish cooling. This two-stage cooling prevents them from cracking while keeping them moist.