Preheat the oven to 350 F.
Grease the sides and bottom of a 9 inch round cake pan. Cut out a circle of parchment paper and place in the bottom of the pan and set aside.
In the bowl of a stand mixer, cream the butter and sugar until light and fluffy. Next mix in the orange zest then the eggs one at a time, mixing thoroughly after each one. Add in the flour and stir again until combined.
In a separate bowl combine the warmed milk and baking powder then incorporate into the batter. Finally, stir together the vinegar and baking soda and mix into the batter as well. Scrape down the sides of the bowl and give the mixture one final stir and pour into the cake pan. Tap gently to remove any air pockets.
Bake at 350 F until a toothpick inserted into the middle comes out clean, between 35-45 minutes.
Place the loaf on a cooling rack, and cool for 15-20 minutes. Run a thin knife around the edge, then invert the cake to remove it and place it right side up on a cooling rack.
Once the loaf is completely cooled, dust with powdered sugar to cover the top. If desired, cut out a paper cross and place on the cake before dusting.
Enjoy!