Preheat the oven and prepare the muffin pan. Preheat the oven to 375°F and move a rack towards the top third. Prepare muffin pans with 18 muffin liners/paper cups.
Make the batter. Combine the softened butter with ¾ cup of the sugar, 2½ tablespoons of the espresso powder and salt in a large bowl. Mix until smooth. In a small dish, whisk the whole egg and egg yolk and then add it the batter with the half and half and vanilla. Mix to blend.Add the flour, baking powder and mini chocolate chips. Mix just until you no longer see dry spots.
Make the topping and assemble. Fill the 18 muffin cups about ¾ the way up. (They will not be smooth and this is okay, as they will even out in the oven. Mix the remaining 2 tablespoons of sugar with the remaining ½ teaspoon of espresso powder and sprinkle a bit on each muffin.
Bake, cool and serve. Bake in the preheated 375°F oven until they begin to crack on top, about 30 minutes. Let them cool in the muffin tins for at least 15 minutes before serving.