Butter two 4 oz ramekins and preheat oven to 425°F.
Melt together the chocolate + butter.
Let cool slightly.
Whip the egg, egg yolk, and coconut sugar for 5–7 minutes until VERY thick and pale.
Gently fold the chocolate mixture into the eggs in thirds.
Sift in cornstarch and fold just until combined.
Don’t overmix.
Chill batter for 20–30 minutes for the perfect molten center.
Bake for 7–10 minutes until edges are set but center still jiggles slightly.
