heat oven to 350 F and grease a 24 to 30 cup mini muffin pan with nonstick cooking spray
whisk flour sugar cocoa baking soda and salt in a large bowl
bring butter water and cocoa to a simmer in a saucepan then pour into the dry ingredients and stir until smooth
whisk in sour cream eggs and vanilla until fully combined
fill each mini muffin cup about 2 3 full and bake until the tops spring back and a toothpick comes out with a few moist crumbs about 10 to 12 minutes.
Ice and Set
while bites bake melt butter with cocoa in a saucepan over medium low heat then stir in milk and remove from heat
whisk in powdered sugar and vanilla until smooth and pourable adding 1 to 2 tsp extra milk if needed
spoon warm icing over warm bites and top with pecans if using
cool 10 to 15 minutes until icing sets then remove bites from the pan and serve.
Notes
1. use full fat sour cream for best texture 2. substitute buttermilk or plain Greek yogurt for sour cream 3. for a thinner icing add milk 1 tsp at a time 4. store airtight at room temperature up to 2 days or refrigerate up to 5 days