Combine lemon juice, egg yolks, sugar, salt, and lemon zest in a saucepan.
Heat over medium-low heat until thickened, then remove from heat and stir in butter until melted.
Chill in the fridge until set.
**For the Lemon Cake:**
Preheat the oven and prepare a baking pan.
Whisk together dry ingredients, then cream butter and sugar until fluffy. Add eggs and vanilla, then mix in dry ingredients and buttermilk. Fold in lemon zest.
Bake until a toothpick comes out clean, then cool completely.
**For the Lemon Cream Cheese Frosting:**
Beat butter until fluffy, then add cream cheese and beat until smooth. Mix in powdered sugar and lemon zest until creamy.
**Assembling the Cake:**
Poke holes in the cooled cake and pipe lemon curd into them.
Frost the cake with lemon cream cheese frosting and swirl in more lemon curd.
Serve and enjoy every citrusy bite of this delightful lemon curd cake!