Step 1: Preheat your oven to 325°F (165°C) and grease a 2-quart baking dish or pudding mold thoroughly with butter.
Step 2: In a medium bowl, whisk together the flour, baking soda, ground ginger, and cinnamon until well combined.
Step 3: In a large mixing bowl, cream the softened butter and light brown sugar together until pale and fluffy, then beat in the black treacle and fresh ginger.
Step 4: Add the eggs one at a time to the butter mixture, beating well after each addition to ensure the batter is smooth.
Step 5: Gradually fold in the dry ingredients, alternating with the whole milk, starting and ending with the flour mixture until just combined.
Step 6: Pour the batter into the prepared dish and bake for 45-50 minutes, or until a skewer inserted into the center comes out clean.
Step 7: While the sponge is baking, prepare the sauce by combining heavy cream, granulated sugar, orange zest, and orange juice in a small saucepan.
Step 8: Simmer the sauce over medium-low heat for 10 minutes until slightly thickened, then stir in the vanilla extract.
Step 9: Remove the sponge from the oven, poke a few holes in the top, and pour half the warm orange cream sauce over the ginger treacle sponge.
Step 10: Serve the ginger treacle sponge with orange cream sauce warm, with the remaining sauce drizzled generously over each individual portion.