Preheat your oven to 180°C (355°F). Line an 8-inch (20 cm) loaf pan with parchment paper.

Add the sugar and lemon zest to a large bowl. Rub the mixture together until the sugar is pale yellow and fragrant.

Add the dry ingredients (flour, poppy seeds, baking powder and salt) to the bowl and whisk until the mixture is well combined. Add all the wet ingredients (milk, oil, lemon juice, and vanilla) and mix until just combined. Some lumps are fine, as long as they aren't lumps of flour.

Pour the cake batter into your prepared pan.

Bake the cake for 55-60 minutes or until you can insert a toothpick in the center and there's no wet batter on it (some moist crumbs are fine). The top of the cake should be golden brown.

Allow the cake to cool in the loaf tin for 10 minutes then transfer to a cooling rack to cool completely.

Add the vegan butter to a large bowl or the bowl of a stand mixer with the paddle attachment. Beat until light and fluffy. Add the sugar, lemon juice and vanilla extract and beat until combined. Add more sugar for a firmer frosting or more lemon juice (or milk) for a smoother frosting.

Dollop the lemon frosting on your cooled loaf cake. If desired, use a small spoon to create swirl patterns on your frosting. Dot some lemon curd on top and swirl it into your frosting (save any leftover lemon curd to serve with the cake). Sprinkle the top with poppy seeds.

Store the cake in an airtight container at room temperature for 1-2 days, or in the fridge for 3-4 days. The frosted cake can be stored in the freezer for up to 1 month.