Put two cups of blueberries, water, and sweetener in a small saucepan. After bringing the ingredients to a boil, turn down the heat to medium. Simmer until the blueberries start to get tender.

Combine 1 tablespoon water and cornstarch in a different, small bowl. Add this mixture to the sauce with blueberries. Cook it for a little longer until the sauce thickens.

After that, turn off the heat and mix in one teaspoon of vanilla essence in the saucepan. Before using, let the blueberry sauce cool.

First, line an 8-by-8-inch baking pan with parchment paper and preheat your oven to 350°F (175°C).

Transfer the flour, oats, baking powder, cinnamon, and salt to a medium-sized mixing basin and whisk to blend.

Using a larger dish, thoroughly mix the egg, butter, maple syrup, and vanilla essence.

Combine the wet and dry ingredients and stir until a cohesive dough is formed. Half of this dough should be reserved for the topping.

To create a solid crust, press the remaining dough into the bottom of the pan that has been prepared.

Cover this crust with 1 cup of the blueberry sauce you made previously, then top with 1 cup of fresh blueberries.

Scatter the reserved dough on top of the blueberry layer.

Bake for about 30 minutes, or until the top is golden brown, in a preheated oven.

Let it cool completely before slicing into 12 equal squares to serve.