First, spray 2-6 ounce ramekins very well with cooking spray and set them on a mini baking sheet.
Preheat the oven to 350.
In a small bowl, whisk together the sugar, flour, cocoa powder, baking powder, baking soda, and pinch of salt. Set aside.
In a medium bowl, whisk together the egg yolk, milk, oil, vanilla, and water
Add the dry ingredients in two batches to the wet ingredients, and stir gently to combine.
Divide the mixture between the two ramekins.
Bake for 20 minutes, or until a toothpick inserted comes out clean.
While the cakes cool, makes the frosting; whisk together all ingredients, adding more milk to think it out to a pourable consistency. Sprinkles!