Yield: 10 mini cakes
Preheat oven to 350 degrees F. Line 18 x 13-inch baking sheet pan with parchment paper and lightly mist with non-stick spray.
Sift together flour and cocoa. Set aside.
Separate 4 eggs, placing whites in a medium bowl and yolks in a large bowl. Beat egg whites until foamy. Slowly add 3/4 cup sugar and beat until mixture is shiny and thickened. Set aside.
Beat yolks with remaining 1/2 cup sugar until mixture is thick and pale in color. Add remaining whole eggs and beat until well combined. Add white eggs to yolk mixture and fold to combine.
Add dry flour mixture to mixing bowl and fold to combine. Spread cake batter in an even layer on prepared baking sheet. Bake for 15 minutes until toothpick inserted in cake comes out clean. While cake is still warm, brush cake with bourbon. Let cake cool in pan.
Cream together softened butter and powdered sugar. Add caramel, bourbon, and salt. Beat until buttercream is smooth.
Place chopped chocolate in a medium bowl. Bring cream to a simmer over the stove or in the microwave. Pour hot cream over chocolate. Let sit undistributed for 2 minutes. Use a sturdy spatula or whisk to stir mixture together until homogenous and smooth. Mixture will thicken as it cools.
Spread bourbon caramel buttercream in an even layer over cooled chocolate cake. Place in the freezer for 10 minutes for buttercream to firm up.
Slice cake crosswise into thirds. Stack layers on top of each other. Trim edges, if necessary. Cover cake and let chill in the fridge for at least 1 hour up (overnight is best).
Slice cake in half lengthwise and divide each half into 5. You should end up with 10 mini cakes. Pour chocolate glaze over each mini cake. Drizzle caramel sauce on top, if desired. Top each mini cake with a chocolate square.