Preheat the oven to 350°F (177°C). Line an 8×8-inch or 9×9-inch baking pan with parchment paper, ensuring that it overlaps the sides for easy removal later.

Cream the softened butter, granulated sugar, and brown sugar together in a large bowl until smooth and fluffy, about 2-3 minutes.

Add the eggs and vanilla extract to the creamed mixture, mixing until well combined and slightly thickened.

Whisk together the flour, baking powder, cream of tartar, and salt in a separate bowl.

Combine the dry and wet ingredients gradually, mixing until just combined. Fold in the white chocolate morsels.

Mix the granulated sugar and cinnamon together in a small bowl.

Spread half of the blondie batter evenly into the prepared pan.

Sprinkle the cinnamon-sugar mixture evenly over the batter.

Dollop the remaining batter over the cinnamon-sugar layer, gently spreading it to cover completely.

Bake for 28–35 minutes, or until the edges are lightly golden and a toothpick inserted in the center comes out clean.

Cool completely before slicing.