Preheat the oven to 325°F and line a 12-cup muffin tin with parchment paper muffin liners

In a large bowl, whisk together the butter and brown sweetener until well combined

Add the eggs, Greek yogurt, vanilla extract, and espresso, and whisk until smooth

Add the almond flour, cocoa powder, baking powder, salt, and espresso powder. Mix with a rubber spatula until fully combined and no dry spots remain

In a microwave-safe bowl, add the sugar free chocolate chips and coconut oil. Microwave in 30-second increments, stirring between each one, until melted and glossy (about two 30-second rounds plus a final 15 seconds)

Let the melted chocolate cool for a few minutes so it's warm, not hot

Pour the melted chocolate into the batter and mix until well combined with no streaks

Using a 2.5 tablespoon ice cream scoop, add 2 scoops of batter to each muffin liner

Give the muffin tin a firm tap on the counter to help the batter settle

Bake for 40 to 45 minutes, or until a toothpick inserted into the centre of a muffin comes out clean

Allow the muffins to cool completely before serving