2CAKE: Make sure rack is in center of oven and preheat oven to 350*F. Butter 2- 9" round cake pans with sides at least 2 inches high. Dust pans with flour.
Stir Chopped unsweetened chocolate in top of double boiler over simmering water until melted and smooth. Set aside to cool. Sift cake flour, unsweetened coco powder, baking soda & salt into medium size bowl. Beat unsalted butter in large bowl (kitchen Aid) until fluffy. Gradually add brown sugar beating until well blended. Add eggs 1 at a time, beating well after each addition and scraping down sides of bowl occasionally. Mix in dry ingredients alternately with sour cream, beginning and ending with dry ingredients. Mix in melted Chocolate & Bourbon Vanilla Extract. Mix in 1 C. boiling water and blend well. Divide batter evenly between prepared pans.
Bake until tester inserted into center comes out comes out clean, about 35 minutes. Cool cakes in pans on wire racks about 10 minutes. Turn cakes out onto racks and cool completely. (cakes can be baked 2 days ahead , Please make sure if you do bake them 2 days in advance they are wrapped tightly in plastic & refrigerated.
Using electric mixer, beat frosting until stiff peaks form. Add 1 T. bourbon and beat until blended.
Cut each cake layer in half horizontally. Place 1 cake layer on platter, brush with 2 T. bourbon, spread 1 C. frosting over layer, repeat with 2 more cake layers brushing each with 2 T. bourbon and spreading each with 1 C. frosting. Top with remaining cake layer. Brush top layer with remaining 2 T. bourbon. Spread Top & Sides of cake nicely with frosting, so it looks pretty "presentation is important too" (Cake can be prepared 8 hours ahead. Refrigerate).