Make the ganache centers first. Heat the heavy cream in a small saucepan until it just begins to simmer, then pour it over the chopped sugar-free dark chocolate in a bowl. Let it sit for 1 minute, then stir until completely smooth.
Spoon the ganache into 10 small mounds on a parchment-lined plate or into a silicone candy mold. Freeze for at least 30 minutes until solid. Preheat your oven to 350F and line 10 cups of a muffin tin with parchment liners.
In a large bowl, whisk together the almond flour, cocoa powder, erythritol, baking powder, and salt until no lumps remain.
Add the eggs, melted butter, sour cream, and vanilla extract. Stir until you have a thick, smooth chocolate batter. Fold in the sugar-free chocolate chips.
Divide half of the batter among the 10 lined muffin cups. Place one frozen ganache disc in the center of each, then spoon the remaining batter on top, making sure the ganache is fully covered.
Bake for 18 to 20 minutes. The tops should be set and slightly cracked, but the centers should still feel soft when gently pressed. Do not overbake or you will lose the molten center.
Let the muffins cool in the tin for just 3 to 4 minutes, then serve immediately while the centers are still gooey and flowing.
