Prepare the loaf pan. Heat a conventional oven to 350°F (175°C). Lightly grease a 9 x 5-inch metal loaf pan and line the base and long sides with parchment, leaving lifting handles. Wash and dry fresh cranberries, halving large berries. Wash, dry, and zest the orange before measuring its juice.

Distribute the orange zest. Rub the orange zest into the measured sugar with clean fingertips until evenly fragrant. Whisk this sugar with flour, baking powder, and salt in the larger bowl. Break up any lumps in the raising agent before liquid is added. The dry mixture should look evenly combined rather than showing distinct streaks of sugar and flour.

Combine the wet mixture. Whisk eggs, milk, measured orange juice, oil, and vanilla in a second bowl. Whisk until the oil is dispersed. Keep the measured juice at ¼ cup even if the orange produces more, saving extra juice for another use rather than adding it to the loaf.

Fold and fill. Fold the wet mixture into the dry ingredients until a few flour streaks remain, then fold in the cranberries. Stop as soon as there are no dry pockets. Spread the thick batter in the prepared pan and level gently. Avoid vigorous beating or repeatedly pressing the berries, which can smear juice through the entire loaf.

Bake and check the middle. Bake about 55–65 minutes, allowing more time if frozen fruit keeps the middle cool. The top should spring back gently, and a tester inserted deep into the center should show moist crumbs without wet batter. Check between berries. Loosely tent with foil if the surface browns before the center is ready.

Cool before slicing. Rest in the pan for 15 minutes, then lift the loaf onto a rack using the parchment. Let cool at least another 45 minutes before slicing; a large loaf may need longer to cool completely for wrapping. Cut with a serrated knife using gentle strokes rather than pressing down through the tender cranberry-filled crumb.