Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish. Arrange frozen pancakes evenly in the dish, overlapping slightly.

In a large mixing bowl, whisk together eggs, milk, sugar, and vanilla until smooth. Pour mixture over pancakes, ensuring they are covered. Let soak for at least 10 minutes.

Cover with plastic wrap and refrigerate overnight, or for at least 30 minutes.

Remove from refrigerator and let sit at room temperature for 10 minutes. Bake for 45 minutes, or until egg custard is set and tops are golden brown.

While baking, mix flour, brown sugar, butter, and cinnamon together until crumbly. After 45 minutes, sprinkle this over the bake and return to the oven for 10 minutes.

Let cool for a few minutes before slicing into squares. Serve warm with syrup or fresh fruit.