Add 90g water and 40g sugar to a pot. Heat over low heat, stirring gently with a spoon or chopsticks until the sugar dissolves completely. Once the syrup is ready, remove it from heat and let it cool to room temperature.

Crack 1 egg into a large, clean bowl. Add 80g condensed milk, 10g honey, and 50g vegetable oil. Using a hand whisk, stir at medium-low speed for 2-3 minutes until the mixture is smooth and emulsified, with no visible oil separation.

Sift 50g cake flour and 3g baking soda together. Gradually add them to the wet mixture. Gently mix with a whisk until the batter is smooth and free of lumps.

Pour the cooled syrup into the batter and mix until fully incorporated. Cover the bowl with plastic wrap and let it rest in a warm place for 40 minutes. Small bubbles will form on the surface, a sign that the batter is ready(just take a look at the image below).

Brush vegetable oil evenly inside your cake mold to prevent sticking. Line the bottom with parchment paper. Pour the rested batter into the mold, filling it about halfway to allow space for the cake to rise.

Preheat your oven to 200°C (top and bottom heat). Place the mold in the center of the oven and bake for 20 minutes. Check for doneness by inserting a toothpick into the center; if it comes out clean, the cake is ready.

Remove the cake from the oven and let it cool completely on a wire rack. Run a knife along the edges of the mold, then invert it onto a plate to release the cake.