• Preheat oven to 350F. Spray and line a 9x9 baking dish with a long piece of parchment paper (optional) so you can lift the cake out for slicing.
• Cream the butter, sugar, and orange zest until light and fluffy.
• Scrape down the bowl and beat in the egg and vanilla. Scrape down the bowl again.
• Whisk together your dry ingredients to combine in a separate bowl.
• Mix the warm water with the molasses in a bowl or glass measuring cup.
• With the mixer on low, alternately add the dry ingredients and molasses mixture, beating after each addition, beginning and ending with the dry.
• Scrape down the sides and make sure to get your spatula down to the bottom of the bowl. Then give the batter a final mix.
• Turn the batter into your prepared pan and smooth out the surface. Bake for 40-45 minutes or until your toothpick inserted in the center comes out without wet batter on it (moist crumbs are fine.) The cake will be nicely risen, and starting to form cracks along the sides. Note: try to first check your cake through the oven window instead of opening the door, which can cause the cake to fall.
• Let cool for 10-15 minutes before lifting out of the pan to finish cooling on a rack. If you did not line your pan you can leave the cake in the pan to cool.
• Only slice your cake when you are ready to serve, otherwise, leave it whole. Serve warm or at room temperature, with or without the custard sauce.

to make the custard sauce

• In a medium bowl whisk the egg yolks, sugar, and vanilla until smooth.
• In a medium heavy bottomed saucepan heat the half and half until scalded, but not boiling. It will start to smoke and little bubbles will appear along the edges.
• Drizzle some of the hot half and half into the egg mixture, while whisking constantly. Then pour that back into the pan and continue to cook, whisking or stirring constantly, until the sauce thickens and comes to a boil.
• Remove from the heat and strain through a fine mesh strainer to remove any stray lumps. 
• The custard can be served warm or cold. If you'd like to serve the custard chilled, you can speed the process by placing it in a a large bowl filled with ice.