Preheat your oven to 350°F (175°C) and butter the bottom and sides of a 9x9-inch baking dish.

Spread softened unsalted butter evenly on one side of each slice of day-old bread and cut into triangles.

Arrange half of the buttered bread triangles in the bottom of the baking dish, buttered side up, then sprinkle half of the raisins over.

Layer the remaining bread triangles on top, buttered side up, followed by the rest of the raisins.

In a mixing bowl, whisk together the eggs and sugar until pale and frothy, then gradually add milk, cream, vanilla, cinnamon, nutmeg, and salt.

Pour the custard mixture evenly over the bread and raisins, gently pressing down to soak, and let rest for 15 minutes.

Bake in the preheated oven for 45-50 minutes until golden brown and a knife inserted in the center comes out clean.

Allow to cool slightly before serving warm, optionally topped with powdered sugar or a scoop of vanilla ice cream.