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Lemon Blueberry French Toast Casserole

French toast is a brunch and breakfast favorite, but standing over the stove preparing individual pieces for a group is challenging. The casserole version of French toast is an easy way to solve this problem, and you can flavor it in so many ways.
Cook Time 30 minutes
Total Time 9 hours 5 minutes
Course Breakfast
Cuisine French
Servings 8 people
Calories 4087.9 kcal

Equipment

  • 1 Baking Dish 9x13-inch
  • 1 Large Pitcher
  • 1 Immersion Blender Alternatively, a regular blender or whisk for custard
  • 1 Mixing Bowl For the lemon glaze
  • 1 Whisk For mixing the glaze

Ingredients
  

Main

  • 4 tablespoons salted butter at room temperature
  • 12 slices potato bread cut diagonally into triangles
  • 8 large eggs beaten
  • 2 cups milk
  • 2/3 cup brown sugar
  • 1/2 cup mascarpone
  • 2 tablespoons vanilla extract
  • 2 lemons 1 zested and halved, the other halved and sliced, for garnish
  • 1 cup frozen blueberries
  • 1 1/2 cups sifted powdered sugar plus more for dusting

Instructions
 

  • Butter a 9-by-13-inch baking dish. Shingle the bread in the baking dish in two rows lengthwise.
  • Add the eggs, milk, brown sugar, mascarpone, vanilla and lemon zest to a large pitcher. Using an immersion blender, blend until smooth. Pour the custard over the bread. Add the frozen blueberries over the top. Wrap and refrigerate overnight.
  • When ready to bake, preheat the oven to 350 degrees F.
  • Uncover the casserole and bake until the custard is set and the bread has crisped, 40 to 45 minutes.
  • Meanwhile, make the glaze by adding the juice from half of the zested lemon to the powdered sugar in a bowl, mixing until smooth. Cover and set aside until ready to serve.
  • Remove the French toast from the oven and drizzle over the lemon glaze. Dust the top with powdered sugar and garnish with the sliced lemons. Serve warm.

Notes

For best results, ensure the casserole refrigerates overnight to allow the potato bread to fully absorb the custard, leading to a richer texture. While potato bread offers a unique tender crumb, challah or brioche can be substituted for an even more decadent version. When preparing the lemon glaze, gradually add the lemon juice to the powdered sugar until a smooth, pourable consistency is achieved – you may not need all the juice. Avoid overbaking to keep the French toast casserole moist and tender; a slight jiggle in the center indicates it's perfectly set.