Measure out the blackberries, clean and dry them and set them aside.
Preheat the oven to 350F and prep an 8×8 square pan by lining it with parchment paper.
To a small bowl, add the flour, baking powder, and ground cinnamon. Whisk to combine and set aside.
To a medium bowl, add the melted butter and cane sugar. Whisk the butter and sugar together until well combined -one to two minutes.
Add the yogurt and vanilla extract. Whisk until all ingredients are well combined – about 1 minute.
Add the dry ingredients to the wet ingredients, folding until almost all of the flour is absorbed. Toss in the blackberries, folding them in until well distributed.
Pour the batter into the prepared pan, making sure to spread it out evenly.
Combine the turbinado sugar and cinnamon in a small bowl and sprinkle the mixture over the top of the blondie batter.
Bake for 35 to 40 minutes or until the blondies are set, edges are slightly browned, and a toothpick inserted in the center comes out clean.
Allow the blondies to rest in the pan for 20 to 30 minutes before transferring them to a cooling rack.
Store the blondies in an airtight container at room temperature.