Preheat oven to 350°F (175°C)
Grease a baking dish (about 8×8 inches or similar size)
Tear 6–8 cups day-old bread into bite-size pieces (about 1-inch cubes)
In a bowl, whisk together 4 large eggs, 2 cups milk, 1 cup heavy cream, 1/2 cup sugar, 2 tsp vanilla extract, 1/2 tsp ground cinnamon, and a pinch of salt
Optional: add 1–2 cups raisins and/or 1–1 1/2 cups chocolate chips
Pour custard over bread and gently press to submerge
Let sit 10–20 minutes to soak (or refrigerate 30 minutes to overnight)
Sprinkle optional topping: 2 tbsp sugar and/or 2 tbsp melted butter over the top
Bake 35–50 minutes, until puffed and set in the center and a knife inserted comes out mostly clean
Rest 10–15 minutes before serving