In a small sauce pan over medium heat, combine the blueberries, sugar and water. Stir until combined. Let it continue cooking until the blueberries start to open and it creates a sauce.

Make a slurry by combining the water and the cornstarch. Making sure your blueberry compote is hot, add the slurry (the heat helps activate the corn starch). Stir until it starts to thicken. When you first add the slurry, it will be a light purple. Cook it until it darkens. This means you are cooking out the flavor of the corn starch.

Set aside and let it come to room temperature. Place plastic wrap on top of the blueberry compote to prevent a skin from forming. As it cools down, it will thicken more (you can put it in the fridge, if you desire, to help the cool down process go faster).

Preheat the oven to 350 degrees. Prep a 8x8 or a 9x9 pan by lining with parchment paper and spraying with cooking spray. Set aside.

In a microwave safe bowl, melt the butter.

In a separate mixing bowl, whisk together the flours, baking powder, salt, and cinnamon.

In a medium sized bowl, whisk the melted butter and the sugars until light and fluffy, about 3 minutes.

Whisk in the egg and egg yolk for 30 seconds and then add the vanilla. Whisk just until combined.

Switch to a rubber spatula and fold the dry ingredients into the wet ingredients. Just mix until there are no more signs of flour. Don’t over mix.

Gently fold in the blueberries.

Pour the dough into the prepared pan. Add the blueberry compote to the top of the dough, and with the back a spoon, evenly spread it across the top of the dough. Sprinkle the streusel on top.

Bake for 30-35 minutes until the top is golden brown.

When the dough is done, let it cool completely before cutting. Serve at room temperature.

In a mixing bowl, whisk together the brown sugar, cinnamon, and flour. Add the butter and with your hands, combine everything. You want it to be well incorporated, but not smooth. This can be stored in an air tight container for up to 7 days in the fridge.