Preheat oven to 180°C/350°F (160°C fan) for 20 minutes before starting the batter (Note 9). Place shelf in the middle of the oven.

Cake pans: Grease 3 x 20cm / 8” cake pans with butter, then line with parchment / baking paper. (Note 10 more pan sizes) Best to use cake pan without loose base, if you can.

Whisk flour, baking powder and salt in a large bowl. Set aside.

Beat eggs for 30 seconds on speed 6 of a Stand Mixer fitted with a whisk attachment, or hand beater.

With the beater still going, pour the sugar in over 45 seconds.

Then beat for 7 minutes on speed 8, or until tripled in volume and white.

Heat Milk-Butter: While egg is beating, place butter and milk in a heatproof jug and microwave 2 minutes on high to melt butter (or use stove). Do not let milk bubble and boil (foam is ok). If you do this ahead, cover and keep hot while beating eggs.

Gently add flour: When the egg is whipped, scatter 1/3 flour across surface, then beat on Speed 1 for 5 seconds. Add half remaining flour, then mix on Speed 1 for 5 sec. Add remaining flour, then mix on Speed 1 for 5 - 10 sec until the flour is just mixed in. Once you can’t see flour, stop straight away.

Lighten hot milk with some Egg Batter: Pour hot milk, vanilla, lemon juice and zest and oil into the now empty flour bowl. Add about 1 1/2 cups (2 ladles or so) of the Egg Batter into the Milk-Butter (don't need to be 100% accurate with amount). Use a whisk to mix until smooth - you can be vigorous here. Will look foamy.

Slowly add milk: Turn beater back on Speed 1 then pour the Milk mixture into the Egg Batter over 15 seconds, then turn beater off.

Scrape and final mix: Scrape down sides and base of bowl. Beat on Speed 1 for 10 seconds - batter should now be smooth and pourable.

Pour batter into pans.

Knock out bubbles: Bang each cake pan on the counter 3 times to knock out big bubbles (Note 10 for why)

Bake 23 minutes or until golden and toothpick inserted into centre comes out clean.

Remove from oven. Cool in cake pans for 15 minutes, then gently turn out onto cooling racks. If using as layer cakes, cool upside down - slight dome will flatten perfectly. Level cake = neat layers.

Frost with provided Lemon Frosting, or Lemon Cream Cheese Frosting from this Lemon Blueberry Layer Cake recipe.

Thickening roux: Place flour and sugar in a large saucepan over medium heat. Cook, stirring constantly, for 30 seconds.

Add milk: While whisking constantly, slowly pour the milk in (this ensure it's lump free). As the milk gets hotter, it will start to thicken - stir constantly so the base doesn't catch.

Thicken roux: Cook until the mixture thickens in a thick, dolloping custard - see video for texture. (Note 13 tip)

Cool: Remove from heat and scrape into a bowl. Cover with cling wrap, pressing down onto the surface to prevent a skin from forming. Cool completely (20 min counter then 30 min fridge), but do not let it get fridge cold. (Note 14) It will firm into a very thick paste.

FROSTING - cream butter: Beat butter with either a handheld beater or stand mixer (with whisk attachment) for 3 minutes until it's smooth and changes from yellow to very pale yellow, almost white.

FROSTING - add roux: While beating on speed 5, add the roux one heaped tablespoon at a time. Take about 1 minute to add it all. Once all added, add lemon zest and juice, then whip for 2 minutes until you can see that it is stiff enough to hold peaks liek whipped cream. Do not whip more than 4 to 5 minutes (this will activate starch and make it sticky).

Flip a cake layer upside down (for level surface). Spread with 3 - 4mm / 0.12 - 0.16" frosting. Top with another upside cake layer, spread with ore frosting. Cover with final cake layer then use remaining frosting to cover top and sides.