Chocolate Cake With Mocha Icing

• 3 eggs
• 3 sticks butter (unsalted room temp)
• 1 1/2 sticks butter softened (unsalted)
• 900 gr powdered sugar
• 350 ml buttermilk
• 325 gr sifted cake flour
• 250 gr corn syrup (light)
• 240 ml water
• 220 gr dark brown sugar packed
• 130 gr unsweetened chocolate melted