Brush bottom and sides of a 15 x 10 inch jellyroll pan with vegetable oil; line with wax paper, and oil and flour wax paper. Set aside.
Beat egg yolks at high speed with an electric mixer until thick and pale; gradually add 1/4 cup sugar, beating constantly. Add vegetable oil and almond extract, stirring well. Set aside.
Beat egg whites until foamy; gradually add remaining 1/2 cup sugar, beating until stiff but not dry. Fold into yolk mixture.
Combine flour, baking powder, and salt; gradually fold into egg mixture.
Spread batter evenly into prepared pan. Bake at 350°F for 8 minutes or until center of cake springs back when touched.
Sift powdered sugar in a 15 x 10 inch rectangle on a cloth towel. When cake is done, immediately loosen from sides of pan, and turn out onto towel. Carefully peel of wax paper. Starting at narrow end, roll cake and towel together, jelly roll fashion; cool completely on a wire rack, seam side down.
Mocha Buttercream Frosting: Beat butter at medium speed with an electric mixer until creamy. Add powdered sugar, cocoa, coffee, and vanilla, beating well. If too stiff, add extra coffee to reach desired spreading consistency.
Unroll cake, spread with 1 cup Mocha Buttercream Frosting and carefully re-roll without towel. Place, seam side down, on a serving plate. Spread remaining frosting over cake. Diagonally cut a 1 inch slice from 1 end of cake, and place against top center of cake to resemble the knot of a tree. Score frosting with fork tines to resemble bark. Chill at least 1 hour. Garnish, if desired.