Old-fashioned Milk Chocolate Cake with frosting

• 6 ex eggs
• 450 gr sifted cake flour
• 400 gr granulated sugar
• 240 ml water
• 240 ml buttermilk
• 190 gr unsweetened chocolate
• 130 gr butter (unsalted)
• 110 gr brown sugar (light)
• 20 gr vanilla
• 7 gr baking soda