In a medium saucepan, combine blackberries, lemon juice, lemon zest, and granulated sugar. Add water and bring to a boil over medium-high heat while stirring occasionally. Once boiling, mix in cornstarch and cook for an additional minute until thickened. Remove from heat and set aside.

In a large mixing bowl, whisk together eggs, skim milk, cinnamon, and vanilla extract until well combined. The mixture should be smooth and creamy.

Spread whipped cream cheese on one side of each slice of thick bread. Optionally, spread a thin layer of blackberry compote atop the cream cheese. Top with another slice of bread, cream cheese side facing inward, creating stuffed sandwiches.

In a skillet, melt butter over medium-high heat until bubbly. Dip each sandwich into the egg mixture and place in the skillet. Cook for about 2-3 minutes on each side, or until golden brown.

Remove sandwiches from skillet and place on a plate. Top with warm blackberry compote and dust with powdered sugar. Serve immediately.