Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or nonstick spray to prevent sticking.

In a small saucepan, combine raisins, water, butter, and 1 teaspoon cinnamon. Bring the mixture to a boil over medium-high heat. Continue cooking until the raisins plump and nearly double in size, then remove from heat. This step makes the raisins juicy and prevents them from becoming tough while baking.

In a large mixing bowl, whisk together eggs, whole milk, heavy cream, vanilla extract, sugar, and 1 tablespoon of cinnamon until smooth. Add the raisin mixture, including the liquid, to the custard base.

Stir in the cubed challah bread until every piece is coated in the custard mixture. Allow the mixture to sit for 10 minutes so the bread can fully absorb the liquid.

Transfer the mixture to the greased baking dish. Cover with foil and bake for 50 minutes. Remove the foil and bake for an additional 10–15 minutes, or until the top is golden brown and slightly crisp while the inside remains soft and custardy.

In a small bowl, whisk together powdered sugar, vanilla, milk, and cinnamon until smooth. Adjust consistency by adding more milk if necessary.

Drizzle the glaze over the bread pudding before serving. Serve warm for the coziest experience.