Preheat the oven to 170°C. Prepare a loaf tin with baking paper attached to it.
Massage sugars with lemon zest with your fingers. Whisk the butter with oil and sugar. Mix for 5 minutes or more - until it's fluffy and foamy.
Add one egg at a time while mixing. Mix until fully combined.
Squeeze a few drops of lemon juice into the milk. In another bowl whisk flour and baking powder. Now add ⅓ of flour into the batter, mix on medium speed, add ½ of milk, defrosted red currants, and repeat the process until you add flour as last. Do not over-mix the batter.
Pour the batter into the loaf tin and bake for 50-65 minutes or until the toothpick comes out clean. Take the loaf cake out of the oven and let cool for another 20 minutes.
When the cake is cool, prepare lemon icing. In a bowl mix icing sugar, defrosted red currants, and lemon juice. Add as many ingredients as you like - the consistency should be like American pancake batter. If you prefer thicker icing - use more icing sugar.
Let the cake cool for an hour before serving.
