Heat the oven to 350 degrees F and lightly grease an 8 1/2' x 4 1/2' loaf pan. The pan should be evenly coated so the loaf releases cleanly after its short rest.

In a medium bowl, combine the brown sugar, boiled cider or other liquid, vegetable oil, eggs, and vanilla, then beat until smooth. The mixture should look glossy and unified, with no streaks of egg left behind.

Whisk the flour with the baking powder, baking soda, salt, and cinnamon, then add that dry mixture to the bowl and stir gently until smooth. The batter should look thick and cohesive, and this is the moment to stop mixing before the crumb gets tough.

Pat the grated zucchini lightly with paper towels or a clean kitchen towel, then fold in the zucchini, walnuts, and raisins or currants. The batter should loosen slightly and fall from the spoon in a thick, slow flow rather than splash or pour.

Transfer the batter to the prepared pan, smooth the top if needed, and finish with the brown sugar topping. An even top helps the loaf rise more uniformly and gives the crust a nicer finish.

Bake for 55 to 65 minutes. The loaf is ready when a toothpick inserted into the center comes out free of wet batter, even if the area just under the crust still feels a little sticky.

Cool the bread in the pan for 10 minutes, then turn it out onto a rack and let it cool completely before slicing. The crust should feel lightly springy, and the loaf will cut much more neatly once the crumb sets.

Keep the bread well wrapped at cool room temperature, or freeze it for longer storage. Wrapping after the loaf has fully cooled helps protect the crumb from drying out or turning tacky.