Coffee and vanilla pound cake

Heat the oven to 170°C (340°F), fan assisted.
Beat the eggs and the two sugars until light and creamy. Stir in the Greek yogurt and the vanilla extract, and mix until perfectly incorporated.
Sift together flour, baking powder, and salt and add them into the batter. Stir to remove all the lumps, then finish with the melted butter. Stir well.
Transfer 1/3 of the batter into a bowl and add the cocoa powder dissolved into the espresso. Stir until you get a smooth batter.
Grease a 9x5x3in loaf pan, and line it with parchment paper. Fold the paper so that it sticks to the edges of the pan.
Pour half of the white pound cake batter into the pan. Spoon half the coffee batter into the pan. Finish with the white batter, and then again spoon the coffee batter on top. Now swirl a wooden skewer or a knife through the batter.
Bake the pound cake for about 45 minutes, or until a toothpick inserted in the centre comes out clean.
While the cake is baking, prepare the vanilla syrup. Pour the sugar and the water into a saucepan, add the vanilla and bring to a boil, then let it simmering for about 5 minutes. Turn off the heat and let it cool down.
When the pound cake is ready, remove it from the oven and brush it immediately with the vanilla syrup, while it is still hot. Remove it from the pan and let it cool completely before slicing it.
It keeps well for a few days at room temperature, in a tray or on a cake stand, on the kitchen table.