Line a standard 12-cup muffin pan with 10 parchment paper cupcake liners or silicone liners. Set aside 10 of the macadamia nut halves for garnish.
Grind the remaining nuts in a food processor or blender until they resemble coarse crumbs. Add the avocado oil and continue to process until the mixture becomes a smooth butter.
In a heatproof bowl set over a pan of barely simmering water, combine the macadamia nut butter, chocolate, and coconut oil. Stir until melted and smooth.
Whisk in the sweetener, cocoa powder, vanilla extract, and fine sea salt. Divide the mixture evenly between the prepared cups, filling each one about one-third full. Refrigerate for 15 minutes, then gently press a macadamia nut half into the top of each cup. Sprinkle lightly with flaked sea salt.
Refrigerate until firm, about 1 hour. Store in the refrigerator for up to 2 weeks.
If you want these fat bombs to be a little firmer and able to stay out of the fridge for a few hours, replace the coconut oil with 1/2 ounce of cacao butter. They will travel much better.