Preheat to 350°F (175°C). Line an 8x8-inch pan with parchment paper or grease lightly with non-stick spray.
In a large bowl, cream softened butter, granulated sugar, and brown sugar for 2–3 minutes until light and fluffy. Beat in the egg and vanilla until smooth.
In a separate bowl, whisk flour, baking soda, salt, and cinnamon. Gradually mix dry ingredients into wet until a soft, thick dough forms.
Spread dough evenly into the prepared pan using a spatula or clean hands.
In a small bowl, stir together brown sugar, cinnamon, and melted butter. Drizzle over the dough. Swirl gently with a butter knife—aim for streaks, not full mixing.
Bake for 22–25 minutes until the top is golden and set. The center should be firm and edges slightly pulled from the sides. Cool completely in the pan.
Beat softened cream cheese and butter until smooth. Add powdered sugar and vanilla; continue beating until fluffy and spreadable.
Spread frosting evenly over cooled bars. Chill for at least 30 minutes before slicing into squares.