Preheat oven to 425F. Butter 4 4-oz ramekins. The cakes are baked in a water bath, so put the ramekins in high-sided baking dish that fits them all, and heat a pot of water on the stove. Keep the water simmering while you make the cakes.
Melt the chocolate and butter in a heat-safe bowl over a pot of barely simmering water. Stir frequently and take the bowl off the heat as soon as the chocolate is melted. Whisk in the sugar and salt until combine, about 1 minute. Then add the eggs, put the bowl back over the simmering water, and whisk them in until smooth, about 1 minute. Take the bowl off the heat again; add the liqueur and vanilla. Once everything is smooth and combined, sprinkle the flour over and mix that in.
Divide the chocolate mixture among the ramekins, filling them about 3/4 of the way. (You will have a little of the batter left over.) Put the ramekins and their baking pan in the oven and carefully pour the hot water into the pan until the water level is about half way up the sides of the ramekins. Bake the cakes for 14 minutes, or until the top is just set and looks dry. Remove the ramekins from the water bath and let them cool on a rack for a few minutes. Dust the tops with confectioners' sugar and serve with raspberries.