1. Preheat your oven to 350°F (175°C) and line a 9×13-inch baking dish with parchment paper.
2. In a large bowl, combine melted butter and sugar, whisking until smooth. Add in eggs and vanilla extract, mixing until well combined.
3. In a separate bowl, whisk together flour, baking powder, cinnamon, and salt. Gradually add the dry ingredients to the wet mixture, stirring just until combined.
4. Spread half of the blondie batter evenly into the prepared baking dish.
5. In another bowl, beat the cream cheese with powdered sugar until smooth. Add egg yolk and mix until incorporated.
6. Spread the cream cheese mixture over the blondie layer in the baking dish.
7. Dollop the remaining blondie batter over the cheesecake layer and use a knife to gently swirl the layers together, creating a marbled effect.
8. Bake for 30-35 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.
9. Allow to cool completely before slicing into squares and serving.

Pro Tip: Patience is key! Allowing the blondies to cool ensures clean cuts and helps the flavors meld together beautifully. This is a lesson I learned from my grandmother, who always emphasized the importance of letting flavors develop over time.