Prep the Frosting

• Combine 1/4 cup all-purpose flour, 1 cup granulated sugar, pinch of salt, 1 cup milk, and 1 tsp vanilla extract in a saucepan over medium high heat and whisk constantly over the heat until the mixture thickens to the consistency of a thin pudding. Depending on various factors, this can take up to 10 minutes.
• Once the mixture, which will serve as the base of your frosting, has reached the desired consistency, transfer it to a heat safe bowl. After 5 minutes and the steam has subsided, cover the bowl in plastic wrap, pressing the plastic directly into the surface of the frosting base. This will help prevent it from forming a skin.
• Allow the frosting base to cool completely to room temperature which takes approximately 90 minutes. Alternatively, you can make this mixture a day or two in advance, store it in the refrigerator, then bring it to room temperature before proceeding with the next steps. While the frosting base cools, prepare the cake.

Prepare the Cake

• Preheat the oven to 350F and prepare a 9 x 13 baking pan by greasing it with butter, shortening or non-stick baking spray. Additionally, you can line it with a sheet of parchment paper to help lift out the final cake and further prevent the cake from sticking.
• Next, sift together 2 1/4 cups flour, 1 1/2 Tbs cocoa powder, 1 1/2 Tbs ground ginger, 1 1/2 tsp baking powder, 1 1/2 tsp ground cinnamon, 3/4 tsp ground all-spice, 1/2 tsp ground cloves, 1/4 tsp baking soda, and 1/2 tsp salt in a medium mixing bowl and set aside.
• In another medium bowl combine 2 Tbs fresh ginger or ginger paste, 3/4 cup unsulphured molasses, and 1 1/12 Tbs canola oil, then set aside.
• In a large mixing bowl, using a hand mixer or stand mixer with the paddle attachment, beat together 3/4 cup unsalted butter and 1 cup dark brown sugar for 2 minutes until the mixture is creamy and lightened in color. 
• Beat in 3 large eggs, an egg at a time, scraping down the sides of the bowl as needed to make sure everything’s evenly mixed.
• Then add in half of the ginger / molasses / oil mixture and half of the combined dry ingredients to the large bowl with the butter and sugar mixture and mix until combined, then add in the remaining wet and dry ingredients and mix until just barely combined.  
• Pour the 3/4 cup hot boiling water on top of the cake batter in the bowl and let it sit for a minute. Then whisk the water into the batter until everything is smooth.
• Pour the batter into your prepared 9 x 13 pan and bake at 350F for 30 minutes or until a toothpick inserted comes out clean and/or pressing the top of the cake with your finger the cake bounces back quickly.
• Once the cake is baked, put it on a cooling rack and allow it to completely cool before adding frosting, otherwise the frosting will melt when applied.

Finish Making the Frosting

• Once the frosting base has cooled, add 1 cup of unsalted butter to the bowl of a stand mixer with the paddle attachment.  Beat for 3 minutes until lightened in color and appears fluffy.
• Lower the mixer speed to medium and slowly add the cooled frosting base mixture, one heaping spoonful at a time. Make sure each spoonful is fully incorporated before adding the next, mixing until everything is well combined.
• Scrape down the sides and bottom of the bowl with a spatula so everything is evenly mixed, then stir in 2 tsp molasses and 1/4 tsp cinnamon. Gradually increase the speed to medium-high, whipping the frosting approximately 2 minutes until it’s smooth, light, and airy.  If you run into issues, check out the frosting troubleshooting guide below.
• Use the back of your spatula to work out any air bubbles, then it’s ready to be used.
• Once your cake is fully cooled, spread the frosting out evenly across the top of the cake and decorate with sprinkles as desired.
• Your cake can be enjoyed right away or stored in an airtight container at room temperature for up to 24 hours.  If you want to refrigerate your cake, you can, but it will make the frosting rather firm, so take it out of the fridge at least 30 minutes prior to serving to help the frosting soften up.