In a medium saucepan over medium heat, combine the blackberries, lemon juice, lemon zest, white sugar, vanilla extract, and water. Bring the mixture to a gentle boil, stirring occasionally, then add cornstarch. Reduce heat and let it simmer for about 5–7 minutes until the compote thickens and berries soften.

In a large mixing bowl, whisk together the beaten eggs, skim milk, cinnamon, and vanilla extract until well combined and slightly frothy. Set aside.

Take the thick bread slices and spread an even layer of whipped cream cheese on one side of each slice. Optionally, add a spoonful of blackberry compote on top of the cream cheese before topping with another slice.

In a skillet over medium heat, melt the butter. Dip each assembled sandwich into the egg mixture, coating both sides. Place the sandwiches in the skillet and cook for about 2 minutes on each side until golden brown.

Stack the cooked French toast on a plate, drizzle with warm blackberry compote, and dust with powdered sugar before serving.