In a saucepan over medium heat, combine the blueberries, sugar, and lemon juice.

Cook for about 5-7 minutes, stirring occasionally, until the blueberries start to break down.

In a small bowl, mix the cornstarch with water to create a slurry.

Add the cornstarch mixture to the saucepan and stir well.

Continue to cook for another 3-5 minutes until the compote thickens.

Remove from heat and stir in the vanilla extract if using.

Let cool slightly before serving.