1. Preheat oven to 350°F (176°C) and line a 9 inch square baking pan with aluminum foil or parchment paper.
2. Combine flour, 1 cup (207g) of sugar, baking powder, salt and 1 teaspoon of cinnamon in a large mixer bowl. Set aside.
3. Whisk together melted butter and sour cream in another medium sized bowl.
4. Add vanilla extract and egg to the butter mixture and whisk until well combined.
5. Add wet ingredients to dry ingredients and beat until well combined.
6. Spread about half of the batter into the bottom of the prepared pan.
7. Spread the blueberry jam into an even layer on top of the batter.
8. Crumble the remaining batter and drop over the blueberry jam, forming an even layer.
9. Combine remaining 1 1/2 teaspoons of cinnamon and 1/4 cup (52g) of sugar in a small bowl, then sprinkle over the top of the batter.
10. Bake bars for 20-25 minutes, then remove from oven to cool completely.
11. If you want to add the glaze, combine all ingredients in a small bowl and whisk until smooth. Drizzle the glaze over the bars.
12. Cut bars into squares. They can be stored at room temperature or in the fridge. I loved them both ways.