Preheat the oven to 165 degrees C (330 degrees F).
Grease a 9 x 5-inch loaf pan with Butter (to taste). Sift All-Purpose Flour (220 gram) and Baking Powder (1/2 tablespoon) together, set aside.
Beat Salted Butter (250 gram), Lemon (1) and Caster Sugar (160 gram) until pale and fluffy at medium speed for about 7-8 minutes. Reduce speed, add Vanilla Extract (1 teaspoon). Add Large Egg (4), one at a time beating thoroughly after each addition.
Add in half of the flour followed by the Sour Cream (200 gram) and remaining flour; beat until just incorporated.
Pour in half of the batter into loaf pan, smooth the batter and add Yuzu Marmalade (2 tablespoon) on top, spread evenly with a spatula. Lastly pour in the remaining half of the batter and smooth top again with a spatula.
Bake in the preheated oven for about 70 minutes or until a skewer put into the center of the cake comes out clean.
Leave cake to cool in the loaf pan for 10 minutes, then take it from the rack to cool completely. Enjoy!