Preheat oven to 350°F (175°C). Generously spray a mini muffin pan with nonstick spray and set aside.

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, and salt. Set aside.

In a medium-sized mixing bowl, combine the boiling water, butter, buttermilk (or sour cream), and vanilla extract. Stir until the butter is completely melted. The mixture should cool to lukewarm.

Pour the wet ingredients into the dry ingredients and stir to combine.

Stir in the beaten eggs until well combined and no streaks of flour or eggs are visible.

Use a 1-tablespoon cookie scoop to portion the batter into the prepared mini muffin pans. Bake for 8-10 minutes, or until the tops spring back when lightly touched. Allow the mini bites to cool completely in the pan before transferring them.

Line a baking sheet with parchment paper and place a cooling rack over it.

Place the cooled cake bites on the cooling rack.

For the glaze, combine the milk, butter, and vanilla extract in a small heat-safe bowl. Microwave for 25-30 seconds until the butter is melted. Stir well.

Stir in the cocoa powder until smooth.

In a medium bowl, add the powdered sugar. Gradually stir in the cocoa mixture until the powdered sugar is completely dissolved and the glaze is smooth.

Carefully drizzle or dollop the glaze over the top of the cake bites. You can gently spread it with a small spatula if desired. Allow the glaze to set before serving.