USING A BREAD KNIFE, SLICE OFF TINY SLICES OF THE TOP TO MAKE THE CAKE LEVEL AND FLAT. IF YOUR CAKE IS FLAT AND LEVEL AFTER BAKING THEN SKIP THIS STEP.
USING A 6" ROUND METAL CAKE RING OR BOWL, CUT OUT 2 FULL CIRCLES FROM THE QUARTER SHEET PAN CAKE ON OPPOSITE SIDES AS CLOSE TO THE EDGES AS POSSIBLE. THEN CUT OUT 2 HALF CIRCLES IN THE OPEN SECTIONS OF THE CAKE, USING A KNIFE TO CUT AROUND THE CIRCLES. (SEE PHOTO FOR REFERENCE).
ON A CAKE BOARD OR FLAT PLATE PUT A LITTLE BIT OF FROSTING IN THE CENTER AND PLACE ONE FULL CAKE ROUND ON TOP, PRESSING LIGHTLY.
BRUSH CAKE VERY LIGHTLY WITH 1/2 TABLESPOON SIMPLE SYRUP ON TOP OF THE CAKE.
COVER LAYER WITH FROSTING, SMOOTH FLAT AND TOP WITH A MIXTURE OF FRESH BERRIES, PRESSING LIGHTLY INTO THE FROSTING.
PLACE BOTH HALF CIRCLE CAKE PIECES ON THE EDGE OF THE CAKE AND FILL THE CENTER WITH SMALL PIECES OF LEFTOVER CAKE (NOT THE CUT ROUNDS) UNTIL THE ENTIRE CENTER IS FILLED WITH CAKE ACROSS THE TOP AND SIDES.
REPEAT THE SIMPLE SYRUP AND FROSTING LAYER WITH FRESH BERRIES ON TOP.
USING THE SECOND FULL ROUND PIECE OF CAKE, PLACE ON TOP AND BRUSH WITH SIMPLE SYRUP AGAIN.
COVER WITH THICK LAYER OF FROSTING AND START SPREADING FROM THE TOP TO THE SIDES UNTIL THE ENTIRE CAKE IS COVERED IN FROSTING. KEEP ADDING LAYERS OF FROSTING AND THEN SMOOTH IT OUT FROM TOP TO BOTTOM WITH SIMPLE SWOOSHES. YOU WILL HAVE A LITTLE FROSTING LEFTOVER.
ONCE SMOOTH, DECORATE CAKE TOP AND SIDES WITH FRESH BERRIES.
REFRIGERATE CAKE FOR 8 HOURS OR OVERNIGHT SO IT'S COMPLETELY SET.
CUT CAREFULLY AND SERVE STRAIGHT FROM THE FRIDGE.