Preheat oven to 325°F (160°C). Grease and line two 8-inch (1.3 L) round cake pans. Beat butter with sugar until fluffy; beat in eggs, one at a time. Stir sour cream with instant coffee and vanilla; beat into butter mixture. Sift flour with the cocoa, baking powder, baking soda and salt in a separate bowl; add to butter mixture and mix on low until just combined
On low speed, slowly pour boiling water into batter; mix until smooth (scraping bowl as needed). Stir in 1 cup (250 mL) chocolate chips. Divide evenly between prepared cake pans; smooth tops. Bake for 40 to 45 minutes or until tops spring back when lightly touched. Cool in pans for 15 minutes; turn onto a rack to cool completely before frosting.
Place one cake layer onto a cake stand. Add a layer of frosting; sprinkle evenly with remaining chocolate chips. Top with remaining cake layer; frost top and sides with remaining frosting. Garnish cake with the additional chocolate chips (as desired).
*Fluffy Vanilla Frosting: Beat 1 cup (250 mL) softened butter in a large bowl until very smooth. Add 4 cups (1 L) icing sugar, 1/2 cup (125 mL) whipping cream and 1 tbsp (15 mL) vanilla extract. Beat on low until combined; beat on high for 3 minutes or until very fluffy. Makes 4 cups (1 L).