Step 1For the crepes, place 2 ounces of the chocolate in a metal bowl set over a saucepan of simmering water. Add one-half cup water and heat, stirring occasionally, until the chocolate is completely melted. Cool slightly. In a blender, combine the flour, salt, milk and eggs. Add the chocolate mixture, and blend to make a smooth batter. Strain the mixture into a small bowl. Cover and let stand at room temperature for 1 hour.
Step 2Make the sauce: In a metal bowl set over simmering water, melt the remaining 2 ounces chocolate with the cream. Keep warm.
Step 3Heat a crepe pan or 9-inch skillet over medium heat. Brush very lightly with butter. Add about 2 heaping tablespoons of the crepe batter to the pan and swirl it to make an even crepe. Use a rubber spatula to smooth the edges. Cook 1 1/2 to 2 minutes until set, then flip over and cook a minute or so longer. Turn the crepe out onto a plate lined with wax paper. Repeat with the remaining batter, layering the crepes between sheets of wax paper.
Step 4To serve, place a crepe on a dessert plate and spoon a generous tablespoon of the custard filling along one half. Fold over and repeat with a second crepe on the same plate. Drizzle a little of the chocolate sauce over (add more cream to thin it if necessary). Repeat with the remaining crepes, filling and sauce and serve.