In a large bowl, with an electric mixer; at medium speed, beat together butter, brown sugar, sugar, eggs, and vanilla until creamy. Reduce to low speed; gradually fold in flour and unsweetened baking cocoa just until blended. Stir in vanilla chips and slivered almonds. Divide dough into quarters; shape into an 8" log; 1/2" thickness and slice into 1/2" pieces. Place on ungreased cookie sheets 1" apart. Flatten each slice with a fork, making crisscross marks. Bake in 350 degree oven for 10 to 12 minutes, or until golden brown. Transfer cookies, cool on a wire rack.