Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9-inch square cake pans.

Sift 2 1/3 cups plus 1 1/2 tablespoon flour, 1/2 cup plus 3 tablespoons cocoa powder, baking powder, and salt together in a large bowl.

Beat butter and white sugar together in a bowl with an electric mixer until light and fluffy, about 4 minutes. Add eggs, one at a time, beating well after each addition. Beat in vanilla extract. Add flour mixture alternately with 1 cup plus 1 1/2 tablespoon milk, mixing batter gently between each addition.

Divide batter evenly between the prepared cake pans.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 40 minutes. Cool for 10 minutes in the pan. Invert onto a wire rack to cool completely, about 30 minutes.

Trim tops of cake layers to make sure they are flat. Set 1 layer on a serving platter. Spread jam on top; cover with second layer. Spread chocolate buttercream frosting over top and sides of the cake, reserving about 2 tablespoons frosting.

Pinch off a piece of marzipan the size of a golf ball. Add red food coloring and knead until color is evenly distributed.

Dust a flat work surface with confectioners' sugar and roll out remaining, undyed, marzipan. Cut out a 9-inch square; carefully transfer to the top of the cake.

Roll trimmings of marzipan and cut into four 9x1-1/2-inch strips. Cut 3 rectangular notches into 1 edge of each strip. Press strips onto the sides of the cake, notches facing down; gently press top and strips of marzipan together to adhere.

Roll out red marzipan and cut into squares of varying sizes. Spread a little of the reserved frosting on the back of each square to act as a glue; arrange in a random Minecraft pattern on top of the cake.