Pulse the granulated sugar and orange zest in a food processor until the zest is fully blended in.

The result would be a fragrant, pale-orange sugar.

Whisk the orange sugar and butter until they become light and fluffy. 

Mix in the egg, vanilla, baking powder, and salt. Whisk until the mixture turns smooth and slightly airy. 

Whisk in half of the flour just until it loosens into the mixture.

Then whisk in the buttermilk until smooth. 

Add the remaining flour and whisk lightly.

Stop as soon as the batter comes together to avoid overworking it.

Using a spatula, gently fold the cranberries into the thick batter so they’re evenly distributed.

Spread the batter into the pan and smooth the top.

Sprinkle the surface with sparkling sugar.

Bake for 40-45 minutes or until the cake is golden and a toothpick inserted comes out clean. 

Cool in the pan for 15 to 20 minutes before lifting out or slicing.