Preheat the oven to 350ºF (177ºC). Grease, or line a mini muffin tin with cooking spray. Set aside.
In a saucepan, melt the butter (11 tablespoons) with both sugars (3/4 cup light brown sugar + 1/2 cup white sugar), and decaf coffee crystals (1 teaspoon) over medium-low heat, stirring until smooth. Remove from heat.
Add chocolate chips (1 cup); stir until melted and glossy. If needed, briefly return to low heat to finish melting
Remove from the heat and add chocolate chips. Mix until the chocolate chips are melted. The residual heat will melt the chocolate chips; if not, place on low heat back on the stove.
Off the heat, whisk in cocoa powder (1/2 cup), salt (1/2 teaspoon), and vanilla (2 teaspoons) until well combined.
Add eggs (2) and yolk (1) one at a time, whisking after each addition, just until the yolk dissapears and is fully incorporated.
Gently fold in flour (1/2 cup plus 1 tablespoon) until just combined (do not overmix at this point!). Stir in hot water (2 tablespoons) until batter is smooth.
Use a small cookie scoop, approximately 2 teaspoons, to scoop the batter into the prepared mini muffin tin.
Bake in the preheated oven for 10-20 minutes, until tops are shiny and set but centers are still soft. While still warm, sprinkle with optional flaky sea salt (1 teaspoon) if desired. Sprinkled sparingly so it complements the chocolate without overpowering the sweetness.
Cool in the pan for 2-3 minutes.
Gently remove the 2-bite brownies and place them on a cooling rack to cool completely.
Bake the remaining batter.