• Preheat oven to 350°F.
• Grease the 9x9 (or 10x10) baking pan and dust with flour.
• Combine flour, cinnamon, ginger, baking soda, and salt in a medium bowl.
  2½ cups all-purpose flour, 1½ tsp cinnamon, 1 tsp ginger, ½ tsp baking soda, ½ tsp salt
• In a stand mixer (or with a hand mixer), cream (mix) together the butter and sugar on medium speed until light and fluffy, about 4 to 5 minutes.
  ½ cup unsalted butter, ¾ cup brown sugar
• Add molasses and then eggs one at a time. Mix until completely combined.
  ¾ cup molasses, 2 eggs
• Add flour mixture alternately with milk. (Add about a third of the flour mixture, then a third of the milk, and repeat until all is in the bowl). Mix just until combined. Don't overmix!
  1 cup whole milk
• Pour batter evenly into prepared pan.
• Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
• Cool on a wire rack.
• Top with lemon sauce and sprinkle with grated lemon zest.

Make the Lemon Sauce

• Combine the sugar, butter, cream, lemon juice, and lemon zest in a medium saucepan. Cook over medium heat until butter is melted, stirring constantly
  1 cup granulated sugar, ½ cup unsalted butter, ¾ cup heavy cream, 1 tbsp lemon juice, 2 tsp lemon zest
• Reduce heat to low and simmer for a few minutes. Stir in the cornstarch slurry (2 tbsp cornstarch combined with 2 tbsp water). Continue stirring until slightly thickened. Remove from the heat and let cool for at least 10 minutes (it will continue to thicken as it cools off).
  2 tbsp cornstarch