Devil's Food Layer Cake

4 oz 82% extra-dark chocolate
1 tsp vegetable oil
2 1/4 c all-purpose flour
1/2 c unsweetened cocoa powder
1 1/2 tsp baking soda
1/2 tsp salt
3/4 c unsalted butter, softened
1 1/2 c sugar
4 eggs
2 tsp vanilla extract
3/4 c reduced fat sour cream
3/4 c milk

Frosting:
1 package (12 oz) semisweet chocolate chips
3 c confectioners sugar
1/2 c unsalted butter, softened
1 container (8 oz) sour cream
3 Tbls milk

Cake:
Heat oven to 325. Coat two 9x2 inch round baking pans with nonstick flour and oil baking spray. Coarsely chop chocolate. Place in a small microwave-safe bowl with oil. Microwave on high pwer for 1 minute, stir until smooth. If needed, heat an additional 15 seconds. let cool slightly. In a medium size bowl, mix flour, cocoa powder, baking soda and salt. In large bowl, wiht mixer on medium speed, beat butter and sugar until fluffy, 3 minutes. Add eggs, one at a time, beating after each. Beat in melted chocoalate mixture and vanilla. Place sour cream in a 2-cup capacity measureing cup. Whisk in milk until smooth. On low speed, beat flour mixture into butter mixture, alternating with thinned sour cream, beginning and ending with flour; beat 1 minute. Spread into pans.

Bake at 325 for 35-40 minutes. Check w/ toothpick. Cook cakes in pans on wire racks - 15 minutes. Turn cakes out onto racks; cook completely.

Frosting:
In large glass bowl, microwave chocolate chips on medium power for 30 secodns, stir. Microwave another 30 seconds until completely smooth. Let cool slightly. With mixer, blend 1 1/2 cups of the sugar with butter. Beat in sour cream, milk and then half of the chocolate until smooth. On low speed, beat in remaining sugar until blended; then beat in remaining chocolate. Continue to beat until good spreading consistency, about 1 minute. Slice one of the cooled llayers in half horizonally (insert toothpicks into sides of layer to use as a guide) Repeat with other layer. Gently place one layer, cut side down, on serving plate (layers will be tender). Spread top w/ frosting. Repeat w/ remaining cake layers and frosting, ending with cake layer, cut side down. Frost top and side of cake with remaining frosting. Refrigerate 1 hour until firm.