Preheat oven to 425°F (220°C). Place oven racks in the upper and lower thirds of the oven.

Line two large baking sheets with parchment paper.

In a food processor, pulse together the flour, baking powder, salt, nutmeg, butter, and 1/4 cup of sugar until the mixture resembles coarse meal.

Transfer the mixture to a large bowl.

Stir in the golden raisins and walnuts.

Add the heavy cream and half-and-half and stir until just combined.

Drop 4 mounds of batter (about 1/2 cup each) onto each prepared baking sheet, leaving 1/2 to 2 inches between mounds.

In a small bowl, stir together the remaining 1/4 cup of sugar and the orange zest.

Sprinkle the sugar-zest mixture over the tops of the mounds.

Bake the biscuits, switching the position of the baking sheets halfway through, until puffed and golden, about 20 to 25 minutes total.

Transfer the biscuits to a wire rack and cool to warm, about 10 minutes.