Preheat oven to 350F. Line an 8-inch square pan with aluminum foil leaving overhang and spray with cooking spray, or grease and flour the pan; set aside.
Brownies – In a large microwave-safe bowl, add the butter, chocolate, and heat on high power to melt, about 2 minutes. Stop to check and stir after 1 minute. Heat in 15-second increments until chocolate has melted and mixture can be stirred smooth. Allow mixture to cool momentarily before adding the eggs so they don’t scramble.
Add the eggs, sugar, vanilla, optional coffee, optional espresso granules (neither make brownies taste like coffee and both enhance and round out the chocolate flavor), optional salt, and whisk vigorously to combine.
Add the flour and stir until smooth and combined without overmixing.
Making sure the batter isn’t excessively warm so the Andes don’t melt (if yours seems on the warm side, wait for a minute or two before adding Andes), add the Andes. Working quickly and with a light hand, fold Andes into the batter using a spatula or spoon, making sure not to overwork the batter or the Andes will melt.
Turn batter out into prepared pan, smoothing the top lightly with a spatula as necessary.
Bake for about 24 to 25 minutes, or until center has just set and is no longer glossy. The toothpick test is somewhat unreliable because you may hit melted, gooey Andes, but toothpick should come out clean or with a few moist crumbs, but no batter. Allow brownies to cool in pan on top of a wire rack while you make the topping.
Topping – In a small microwave-safe bowl, add chocolate chips, and heat on high power to melt, about 1 minute. Stop to check and stir after 1 minute. Heat in 15-second increments until chocolate has melted can be stirred smooth.
Evenly pour the chocolate over brownies (they don’t have to be completely cooled), smoothing the top lightly with a spatula or offset knife; set aside on rack while you unwrap and dice the Andes.
After chocolate has cooled for about 8 to 10 minutes, evenly sprinkle the Andes. The chocolate needs to be warm enough so the Andes will melt into it just enough to adhere, but not too warm or they’ll melt completely (not a bad thing in terms of taste, but not what I was going for visually); use your judgment about when to sprinkle them.
Place pan on wire rack and allow to cool uncovered for about 4 hours, or until chocolate has set completely, before slicing. Alternatively, cover with a sheet of foil to prevent fridge smells, and place pan in fridge for about 2 hours, or until sufficiently chilled for slicing. Lift brownies out using foil overhang, slice, and serve. Brownies will keep airtight at room temp for up to 1 week, in the fridge for up to 2 weeks, or in the freezer for up to 6 months. I prefer these brownies slightly chilled and store them in the fridge.