Preheat oven to 350 degrees.
Lightly spray a mini muffin pan with nonstick cooking spray. Set aside.
Combine 1 cup butter, 1 cup water and 1/4 cocoa powder in medium saucepan over medium heat. Cook until butter is melted, stirring occasionally.
Bring to a boil, whisking constantly, then remove from heat.
In a medium bowl, combine sugar, flour, salt and baking soda. Stir to combine.
Stir in buttermilk and 2 eggs. Stir in cooked chocolate mixture and mix until smooth.
Fill prepared muffin pan cups 1/4 full with chocolate batter. {Note: I pour mine into a large measuring cup and then pour it into the pan from there.}
Add 1 tsp of salted caramel sauce. Top with additional chocolate batter until approximately 1/2 full.
Bake in preheated oven for 10 minutes or until toothpick inserted into the center comes out clean.
Meanwhile, prepare frosting by combining 1/2 cup butter, 1/4 cup cocoa and milk in a medium saucepan over medium heat. Stirring constantly, bring to a simmer.
Remove from heat and, working in batches, whisk in powdered sugar and vanilla. Pour over hot cakes. Let set for 5-10 minutes.
Drizzle with additional caramel sauce.