Lemon cake:

• Preheat the oven to 350F and prepare 2 8-9" cake pans with parchment paper and butter
• Massage the lemon zest into the sugar until it looks fluffy. Add the melted butter and oil and whisk for 2 minutes. Then add the eggs and vanilla and whisk for another 1-2 minutes
• Sift in all the dry ingredients and fold to combine
• Lastly, fold in the sour cream and lemon juice
• Divide the batter evenly between the 2 pans and bake for 25-28 minutes until done
• Let the cakes cool in the pans for 10-15 min, then turn onto a wire rack and let cool completely

Lemon curd:

• Mix the water, lemon juice, sugar, cornstarch, salt, eggs and egg yolks in a nonstick pan, and stir and cook on low heat until they form a thick mixture that coats the back of a spoon
• Remove from heat and mix in the butter until combined
• Pass through a fine sieve mesh, cover with cling wrap and refrigerate until fully cooled down

Simple syrup:

• Heat the water and sugar in a saucepan on medium heat until the sugar dissolves. Remove from heat and let cool down fully

Cream cheese frosting:

• Whisk the butter using the balloon whisk attachment of your stand mixer for 5-7 minutes until it is light and fluffy, and almost white in color
• Add the sugar and vanilla, and whisk for another ~5 minutes until well combined
• Add the cream cheese a little at a time, whisking at medium speed, until everything just comes together. avoid mixing too much after the addition of the cream cheese

Assembly:

• Once everything has cooled down, start assembly. Trim off the domes from the cakes (i.e., level them off) and divide each cake into 2 even layers so you have 4 layers total
• Place one layer onto a turn table and brush generously with simple syrup. Add a layer of cream cheese frosting, and pipe it around the edges to create a dam. Fill with a layer of lemon curd
• Repeat until all layers are done. Coat the cake in a thin layer of cream cheese frosting as the crumb coat and let it cool until it is stiff
• Frost the cake with the remaining cream cheese frosting in any decoration style you like, and top off with the remaining lemon curd
• Decorate with candied lemon slices if desired, and serve!