Preheat the oven to 180C/350F and line two 8 inch cake tins with grease proof paper. I like to spray my cake tins with cooking spray and then lay the grease proof over it. You can also use kitchen paper with butter on to grease the pans.
MAKE THE CAKE: Place the butter or margarine, sugar and lemon zest into a large bowl, or the bowl of your stand mixer. Mix on medium-high speed for 2-3 minutes, until light and fluffy.
Add in the eggs and vanilla extract, scraping down the sides as necessary, and mix until well incorporated, around 1 minute on medium-high speed.
Add in the flour, baking powder and salt, if using and mix on low until the mixture starts to coem together. Then gradually add the milk, while continuing to mix. Once all the milk is added, turn the speed up to medium and mix for 30 seconds to make sure everything is well mixed.
Divide the cake batter between your prepared cake tins, I use a 1/2 cup measure to divide the batter to make sure it's even.
Place the cakes into the oven for 25-30 minutes, until risen, golden and an inserted skewer into the centre comes out clean. Leave to cool in the pans completely.
MAKE THE FROSTING: Place the butter, icing sugar, vanilla and salt into a large bowl, or the bowl of your stand mixer and mix on low until the sugar starts to incorporate. This will avoid an icing sugar cloud! When the mixture comes together, turn the mixer up to medium.
Continue mixing for about 1 minute on medium-high speed before stopping to add the milk, 1tbsp at a time. I only needed 1tbsp of milk in this recipe. After you've added 1tbsp of milk mix on medium-high speed for 1-2 minutes. Check the consistency before deciding to add more milk or not. I mix my frosting for so long because it becomes super light and fluffy. You'll be able to tell because the colour gets paler too. You want your frosting to hold its shape, but to be easy to spread. I would say it should be like stiff peak whipped cream.
Place 4tbsp of the frosting into a small bowl and add in 1tbsp of lemon curd. Mix by hand until all the lemon curd is mixed in properly.
Add 3tbsp of strawberry jam to the remaining large bowl of frosting and mix until well combined and your frosting is evenly pink.
TO ASSEMBLE: Remove the cakes from the cake tins. Place them on a cutting board and use a bread knife or cake leveller to level the cakes. Trim any domed top off so the cakes as level as possible.
Take your 1/2 cup of halved strawberries (if using) and pat them dry with kitchen paper. Get as much moisture off of them as you can. Leave to one side.
*It is much easier to do the next steps with an icing turntable* Place a cake board/plate onto the turntable, then place a small dot of the strawberry frosting onto the centre of the board/plate. Place one of your cake layers bottom side down onto the plate/board. Spoon the lemon curd buttercream into the centre of the cake and spread into an even layer.
Either place one layer of halved strawberries on top of the lemon curd buttercream, or spread 3tbsp of strawberry jam onto it.
Take your next cake layer and place it bottom side up. So the flat base is at the top.
This is the way I ice my cakes. Some people place all the frosting on top and then push it down the sides. I don't find that the easiest. You can do it whichever way you want. Spoon around 1/3 cup of the strawberry buttercream into the centre of your cake. Take a small offset spatula and spread the frosting all over the top of the cake and slightly over the edges. No need to be too neat yet, I come back to the top last.
I then take my small spatula and pick up frosting to place on the side. I first go around just filling the gap between the two cakes, then I start adding more frosting to cover the sides entirely. I prefer to add small amounts of frosting many times, than one large lump spread about.
Once you've placed all the frosting and covered the sides of the cake, you can either place the spatula tip down and turn the turntable as you hold the spatula in one place, this will smooth the frosting out. You can also do this step with a cake smoother tool. Or you can swirl the frosting to create a ripple effect. I took my spatula tip side down and did straight lines up to meet the top. It's totally up to you. Once I had gone all around the cake from bottom to top to create my lines. I went back to the top to finish.
I smoothed the top as much as I could, then went around the edge with my spatula at a slight downwards angle to create a smooth, almost bevelled edge. I held the spatula at the edge, at a 5 degree angle downwards and then moved the icing turntable. This will smooth all the frosting from where you've brought the spatula up the sides.
To finish off, melt the white chocolate in a small, shallow bowl. Dry off 10-12 whole strawberries with kitchen paper. Dip/roll each strawberry in the melted chocolate and then place them in the centre of the cake. I did a circle of 6 strawberries in the centre to create a circle and placed one larger strawberry in the middle of my circle. For the next layer, I brought the strawberries in a bit and angled them inwards, I used 4 strawberries for this next layer. To finish I placed one more strawberry in the centre of the layer of 4 to create a "mountain" of strawberries.
Let the chocolate set up for 10-20 minutes before serving. Strawberry Lemon Layer Cake will keep covered, in the fridge for 2 days with fresh strawberries inside, or 4-5 days with jam inside. The strawberries on the top are best eaten within 2 days. If you're doing a jam fililng and need the cake to last, either leave the chocolate strawberries off, or add them just before you need the cake.