Preheat the oven to 350°F and grease a 10 to 12 cup bundt cake pan with butter, then dust with flour.
In a large mixing bowl or stand mixer bowl, beat the eggs and brown sugar until the sugar dissolves completely.
Add vegetable oil, buttermilk, molasses, and vanilla extract, then beat until smooth.
Slowly mix in flour, baking powder, ground ginger, cinnamon, salt, and baking soda until just combined; avoid overmixing.
Pour batter into the prepared bundt pan and bake for 50 to 55 minutes, then remove and allow to cool.
Whisk powdered sugar, milk, and optional vanilla extract to make vanilla icing while the cake cools.
Once cooled, drizzle the cake with the vanilla icing.
Garnish with optional cranberries, rosemary, Christmas sprinkles, nuts, or a cinnamon dusting as desired.