Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, then line the bottoms with parchment paper.

In a medium bowl, whisk together the sifted flour, baking powder, and salt. Set aside.

In a large mixing bowl or the bowl of a stand mixer, cream together the softened butter and granulated sugar on medium-high speed until light and fluffy (about 3-5 minutes).

Add the eggs one at a time, beating well after each addition until fully incorporated. Scrape down the sides of the bowl as needed.

Stir in the lemon zest.

In a separate small bowl, combine the lemon juice and milk.

With the mixer on low speed, gradually add the dry ingredients to the wet ingredients in three additions, alternating with the milk-lemon juice mixture, beginning and ending with the dry ingredients. Mix until just combined, being careful not to overmix.

Divide the batter evenly between the prepared cake pans.

Bake for 28-32 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

In a medium saucepan, heat 1 1/4 cups of the whole milk with 1/4 cup of the granulated sugar over medium heat until it just begins to simmer, stirring occasionally. Do not boil.

In a separate medium bowl, whisk together the remaining 1/4 cup milk, remaining 1/4 cup sugar, lemon juice, egg yolks, and cornstarch until smooth.

Slowly pour about half of the hot milk mixture into the egg yolk mixture, whisking constantly to temper the yolks.

Pour the tempered egg yolk mixture back into the saucepan with the remaining hot milk.

Cook over medium heat, whisking constantly, until the cream thickens significantly and comes to a boil (about 2-4 minutes). Continue to whisk and boil for 1 minute to ensure the cornstarch is cooked through.

Remove from heat and stir in the lemon zest and cold butter until the butter is fully melted and incorporated.

Pour the lemon cream through a fine-mesh sieve into a clean bowl to remove any lumps or cooked egg bits.

Press plastic wrap directly onto the surface of the cream to prevent a skin from forming. Refrigerate for at least 2 hours, or until completely chilled and firm.

In a small saucepan, combine sugar and water. Heat over medium heat, stirring until the sugar is completely dissolved.

Remove from heat and stir in the lemon juice. Let cool completely before use.

In a large mixing bowl (preferably chilled) or the bowl of a stand mixer with a whisk attachment, combine the cold heavy cream, powdered sugar, and vanilla extract.

Beat on medium-high speed until stiff peaks form. Be careful not to overbeat, or it will turn grainy.

Once the cake layers are completely cool, use a serrated knife or cake leveler to level the tops if desired, creating flat surfaces.

Place one cake layer on your serving plate or cake stand. Brush generously with about half of the cooled lemon simple syrup.

Spread a generous layer of the chilled lemon cream evenly over the first cake layer, leaving a small border.

Carefully place the second cake layer on top. Brush this layer generously with the remaining lemon simple syrup.

Using an offset spatula, spread the whipped cream frosting evenly over the top and sides of the entire cake.

Garnish with fresh lemon slices, lemon twists, or a sprinkle of fresh lemon zest if desired.

Refrigerate the cake for at least 30 minutes before slicing and serving to allow the layers to set.