Butter an 8 by 8 by 2-inch glass baking dish. Set aside.

Place the bread cubes in the prepared baking dish. Bring the milk to a simmer in a large heavy saucepan. Remove from the heat. Add the chocolate and whisk until melted and smooth.

Using an electric hand mixer, beat the sugar, eggs, and egg yolks in a medium bowl until blended. Gradually whisk the chocolate mixture into the egg mixture. Add the raisins and cinnamon. Pour the custard over the bread. Let the mixture stand for 1 hour (some custard will not be absorbed). Can be prepared and refrigerated for up to 2 hours ahead.

Preheat the oven to 350 degrees F.

Bake until just set and the center moves slightly when the dish is shaken, about 45 minutes. Dust with powdered sugar and serve warm or at room temperature.