Preheat the oven to 350°F (175°C).
Prepare an 8-inch (20cm)or a 9-inch (22cm) loaf pan by lightly greasing the bottom of the pan and the sides of the baking sheet with oil and line it with an overhang of baking paper.
In a medium sized mixing bowl combine milk & white vinegar. Allow this mixture to sit for a few minutes until it is slightly curdled.
Add oil, and molasses to the milk mixture and mix using a hand whisk until fully combined.
Add cane sugar, light brown sugar and vanilla extract, mix using a whisk until the sugar is dissolved.
In a separate bowl combine all the dry ingredients: all-purpose flour, baking powder, baking soda salt, 2 tbsp of cinnamon and gingerbread spice.
Add dry ingredients to the liquid ingredients in three small additions, whisking in between each addition.
In a heatproof bowl melt dark chocolate, to this add cocoa powder and warm water. Stir this mixture until it is smooth.
Pour 1/3 of the prepared cake batter into the chocolate mixture. Mix gently to get a smooth batter.
Pour half of the gingerbread cake batter into the base followed by all the chocolate batter and top it with the remaining gingerbread cake batter.
Use an offset spatula to make swirls & smooth the top.
Bake the loaf cake for 40-50 minutes, or until the top of the cake is firm to touch and a skewer inserted into the center of the cake comes out with a few crumbs attached.
Cool the cake in the loaf pan for 45 minutes. Then remove from the loaf pan and let it cool completely on a wire rack.