It's best to minimise contact with metal when preparing the lemon curd to prevent it from developing a metallic aftertaste. Therefore, I don't recommend using a metal bowl, metal utensils (such as a metal whisk) or a metal/metal-coated saucepan.Instead, use a glass or ceramic bowl, a rubber spatula or a wooden spoon, and a non-metal saucepan such as one with a ceramic coating.

Add the sugar and lemon zest to a bowl, and use your fingertips to rub the zest into the sugar.Tip: This helps to release more essential oils from the zest and it will make your lemon curd extra fragrant.

Add the egg yolks and salt to the lemon-sugar, and mix or whip them until slightly fluffy and paler in colour (no need to use a stand or a hand mixer for this, just whisk them briefly together by hand with a silicone whisk, a rubber spatula or a wooden spoon).

In a saucepan over medium-high heat, cook the lemon juice until it only just comes to a boil.

Add the hot lemon juice to the egg yolk-sugar mixture in a slow drizzle, mixing constantly until you've added all the juice.Tip: This tempers the egg yolks and reduces the chances of your lemon curd splitting or curdling when you cook it.

Return the mixture to the saucepan and cook it over low heat with constant stirring until thickened so that it thickly coats the back of a spoon or spatula. This should take about 4-5 minutes. Don't allow the lemon curd to come to a boil – you shouldn't see any bubbles forming.

Once thickened, remove from the heat and stir in the butter until it's fully melted.

Pass the lemon curd though a fine mesh sieve to remove the lemon zest – this will make it perfectly smooth and creamy (but you can skip this step if you don't mind the texture of the lemon zest).Tip: I don't recommend using a metal sieve, as contact with metal can give your lemon curd a slight metallic aftertaste. If possible, use a sieve with a plastic or silicone mesh.

Pour the finished lemon curd into a bowl or other heat-proof container and cover it with a sheet of plastic wrap/cling film. Make sure that the plastic wrap/cling film is in direct contact with the surface of the lemon curd – this will prevent skin formation. Allow to cool completely to room temperature. (You can also prepare the lemon curd a day or two in advance and keep it in the fridge until needed.)

Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line a 9-inch (23cm) square baking pan with parchment/baking paper.Tip: When lining the baking pan, I recommend leaving some parchment/baking paper overhang, as that will help with removing the cake from the pan later on.

Add the sugar and lemon zest to a large bowl, and use your fingertips to rub the zest into the sugar. Tip: This helps to release more essential oils from the zest, and it will make your cake even more lemony and aromatic.

Add the buttermilk, melted butter, oil, eggs and vanilla, and whisk well until combined.

In a separate bowl, whisk together the gluten free flour blend, almond flour, baking powder, baking soda, xanthan gum and salt, and add them to the wet ingredients.

Whisk well until you get a smooth cake batter with no flour clumps.

Transfer the batter into the lined baking pan and smooth out the top.

Dollop about ⅔ of the lemon curd evenly over the batter. (You can use the rest of the lemon curd for serving with the baked cake.)

Use a knife, the handle of a spoon or a skewer to swirl the lemon curd around. The more you swirl it, the more it will become mixed into the cake batter, so don’t overdo it. However, if you leave any large blobs of un-swirled lemon curd, they will sink down into the batter as it bakes and rises, and you’ll get rather dramatic “trenches” in your cake. (I like a mix of both, for a lovely, rustic-looking cake.)

Sprinkle the top of the cake evenly with the granulated sugar.

Bake at 350ºF (180ºC) for about 22-24 minutes or until the cake is well-risen, golden on top (with a few dark golden-brown caramelised patches) and an inserted toothpick comes out clean. The lemon curd will puff up a bit in the hot oven and it will then collapse as the cake cools.

Allow the cake to cool in the baking pan for about 10-15 minutes, then transfer it out of the pan onto a wire rack to cool.

Serve warm or cooled completely to room temperature, with an extra dollop of lemon curd.

The gluten free lemon curd cake keeps well in a closed container in a cool dry place for about 3-4 days.

You can store the leftover lemon curd in an airtight container in the fridge for up to about 10 days.