Super moist chocolate cake with super smooth caramel frosting

1 pc whole egg
1/2 cup oil
1 cup milk
2 cups brown sugar
2 cups all purpose flour
2/3 cup unsweetened cocoa powder
1 tsp baking powder
2 tsp baking soda
1/2 tso salt
1 cup hot water
1/2 tbsp instant coffee
Bake @ 300°F PREHEATED OVEN for
25 minutes
FOR CARAMEL FROSTING:
2 cans evap milk (410ml each can)
5 pcs egg yolk
1 cup brown sugar
1/4 cup cornstarch
1/2 tsp salt
2 tbsp unsalted butter