Preheat the oven to 375 degrees F.
Melt chocolate and butter together, making sure chocolate is melted and smooth. Set aside to cool slightly.
In the bowl of a standing mixer, beat the eggs, yolks, and sugar at medium speed for 5 minutes. Add the vanilla, bourbon (if using), and salt, and mix to combine. Add the flour and mix until the flour is completely incorporated. Add the slightly cooled chocolate and butter, and mix lightly.
Fill 6 ramekins (or two oven safe bowls, see above note) halfway and place them on a baking sheet. Bake 11-12 minutes. The edges should be starting to bake up, but the center should still look underdone. Let the cakes cool a few minutes, and then serve alone or with basil ice cream.