Roti Bakar Perancis Croissant Kayu Manis Panggang

Bahan-bahan (4 porsi)

• 3 large croissants, a few days stale
• 3 eggs
• 3/4 cup milk
• 3 tablespoons Greek yogurt
• 1/4 cup sugar
• 1/2 tablespoon vanilla extract
• 3 tablespoons flour
• 1/4 cup brown sugar
• cinnamon to taste (I used almost a full teaspoon)
• pinch of salt
• 3 tablespoons cold butter, cut into small pieces