Preheat your oven to 350°F (175°C) and prepare a 9×13 inch baking pan by greasing it with non-stick cooking spray or lining it with parchment paper.

In a medium-sized bowl, whisk together the flour, ground ginger, cinnamon, nutmeg, cloves, and baking soda.

In a large bowl, cream the softened butter and brown sugar until fluffy.

Blend in the molasses and vanilla extract, followed by the egg and egg yolk. Mix thoroughly.

Gradually incorporate the flour mixture into the butter mixture, mixing half at a time.

Spread the cookie dough into your prepared pan, using non-stick spray on your hands if necessary.

Bake in the preheated oven for 22-25 minutes, or until the edges start to pull away and a toothpick inserted in the center comes out clean.

Allow the bars to cool completely in the pan before frosting.