Preheat & Prep Pan:
Preheat oven to 350°F (175°C). Grease a 5×9-inch baking pan and line with parchment paper.

Mix Dry Ingredients:
In a medium bowl, whisk together flour, baking soda, ginger, cinnamon, and pumpkin pie spice.

Warm Liquids:
In a small saucepan, heat milk and brown sugar until sugar melts and mixture is lukewarm. In another saucepan, warm molasses and corn syrup until lukewarm.

Cut in Butter:
Add cold, cubed butter to the dry flour mixture. Use a pastry blender or your fingers to work it in until crumbly.

Combine Wet & Dry:
Pour warm milk mixture into the flour mixture, stirring gently. Add warm molasses mixture and stir again. Whisk in the egg until fully incorporated.

Bake:
Pour batter into prepared pan. Bake for about 45 minutes, or until a toothpick inserted in the center comes out clean.

Cool & Rest:
Cool completely in the pan. For best results, wrap the cooled cake in foil and let it sit overnight to allow the top to become sticky and rich.

Prepare Frosting:
In a bowl, beat cream cheese and softened butter until creamy. Add vanilla and cinnamon. Gradually beat in powdered sugar until smooth. Mix in molasses. Chill before using.

Frost & Serve:
Once cake has rested overnight, frost with the chilled cinnamon molasses frosting. Slice and serve.