Preheat your oven to 350 degrees
Prepare an 8” or 9” round cake pan by generously greasing it and lining the bottom of the pan with parchment paper
In a large bowl, combine 8 tablespoons of room temperature butter, 1 large egg, 1 large egg yolk, 1/2 cup of granulated sugar, 1/2 cup of brown sugar and 2 teaspoons of vanilla extract and whisk until creamy
Add 1 cup of all purpose flour, 1/3 cup of unsweetened cocoa powder, 1 teaspoon of espresso powder, 1/2 teaspoon of baking soda and 1/4 teaspoon of salt and mix until just combined
Gently fold in 3/4 cup milk chocolate chips, 1/2 cup of dark chocolate chunks and 1/2 cup of toffee bits
Press the cookie dough into the prepared pan
Bake on a center set rack of a 350 degree oven for 25-30 minutes or until the outer edges feel set and the center barely jiggles
Transfer the pan to a cooling rack and allow the cake to cool fully before removing it from the pan
Decorate with a light sprinkle of flaky sea salt, some chocolate buttercream and some chocolate sprinkles
Store in airtight container at room temperature or wrap tightly in plastic and freeze