Remove the crusts from the bread slices. Spread one side of each slice evenly with softened butter, then cut each slice diagonally to form triangles.

Arrange a single layer of the bread triangles, buttered side facing up, in a well-greased 9×9-inch baking dish.

Sprinkle half of the raisins and half of the cinnamon evenly over the bread layer. Repeat with a second layer of bread, followed by the remaining raisins and cinnamon.

In a saucepan over medium heat, warm the milk and heavy cream until heated through. Do not allow the mixture to boil.

In a separate bowl, whisk together the eggs and granulated sugar until fully combined.

Slowly whisk a small amount of the warm milk mixture into the egg mixture to temper the eggs. Gradually add the tempered egg mixture back into the saucepan with the remaining milk, whisking continuously. Remove from heat.

Carefully pour the custard mixture evenly over the bread layers. Allow the dish to rest for approximately 30 minutes so the bread can fully absorb the custard.

Preheat the oven to 350°F (175°C). Bake the pudding for 30 minutes, or until the top is golden brown and the custard is set.

Remove from the oven and allow to cool slightly before serving. If desired, sprinkle lightly with additional granulated sugar before serving.