Wrap a sweet potato with a sheet of aluminum foil. Bake it at 190℃ / 374 F for 60-70 mins (no need to preheat). Bake it until soft enough to insert a skewer smoothly.

Use a spoon to scoop out the flesh. (net weight; about 380g / 13.4 oz)

Transfer the sweet potato flesh onto the mash sieve and strain it by pressing with a spoon or spatula. Preheat an oven to 200℃ / 392 F.

Add granulated sugar, unsalted butter, honey, egg yolk, and vanilla oil in order, mix well each time until combined.

Add heavy cream in 3-4 parts and mix well each time until combined.

Divide it into 9 equal and use your hand to form each like sweet potato shape. Put them on a baking tray. (Depending on the water content of the sweet potato, the batter may be too soft for you to shape by hand. In that case, use a spatula or a spoon to put the batter on a baking tray and bake as it is.)

Put egg yolk and 1/2 tsp rum in a small bowl. Mix well until combined. Brush the surface of 9 pieces with the egg mixture.

Bake it at 200℃/ 392 F for 15-20 mins or until golden brown. Brush freshly baked cakes with honey (optional). It's all done!