Mix vegetable oil and sugar together until combined, then add the room-temperature egg and mix well.

Add room-temperature heavy cream and mix until smooth.

Sift cake flour, baking powder, and salt together, then mix into the wet ingredients.

Before the batter is fully mixed, add chopped nuts and fold them in. Finally, mix in the yuzu jam until the batter is smooth.

Fill muffin cups to 80% capacity, then tap the tray on the counter to remove air bubbles.

Bake in a preheated oven at 190–200°C (374–392°F) for about 25 minutes. Check doneness with a toothpick; if it comes out clean, remove the cakes from the oven.