Preheat the oven to 425°F. Thoroughly grease 4 4-ounce ramekins and place them in a casserole dish with high sides.
Melt the chocolate and butter together using a double boiler or microwave. Stir until smooth and set aside to cool slightly.
In a large bowl, whisk together the eggs, yolks, sugar, and vanilla until the mixture becomes pale yellow and thickened (use a mixer for easier whisking).
Gradually drizzle the melted chocolate mixture into the egg mixture, whisking constantly to avoid curdling.
Sift in the gluten free flour, cocoa powder, and salt, folding gently into the batter until just combined.
Pour the batter into prepared ramekins, filling them about 3/4 full.
Add water to the casserole dish until it reaches halfway up the ramekin sides. Carefully transfer to the oven.
Bake for 15 minutes or until the tops are set but still slightly soft in the center.
Cool for 10 minutes before gently flipping the cakes onto plates. Dust with confectioners’ sugar if desired and serve immediately.