Place a rack in the center of the oven, and preheat the oven to 350 degrees F. Grease and flour two 9-inch round cake pans with solid vegetable shortening and flour, and set aside.
Place the egg yolks, ¼ cup of the milk, and the vanilla in a large bowl and whisk to combine. Set aside.
In the large bowl of an electric mixer, combine the flour, sugar, baking powder, and salt. Mix on low just to blend, 15 seconds. Add the soft butter, the remaining ¾ cup milk, and the grated zest and juice of the lemon. Mix on low until the ingredients are moistened, then increase the mixer speed to medium and beat about 1 ½ minutes or until batter is stiff. Scrape down the sides of the bowl. Add the egg mixture to the batter in three batches, beating between additions until the batter is smooth.
Divide the batter between the two pans, and place in the oven. Bake until the cake springs back when lightly pressed in the center, about 25 to 32 minutes. Let the cake layers cool in the pans on racks for 10 minutes, then invert onto the racks to cool completely before icing.
For the Lemon Buttercream Frosting, place the butter in a large bowl of the electric mixer, and mix until the butter is soft, about 1 minute. Add 1 cup of the confectioners’ sugar and the pinch of salt and mix on low to incorporate, about 15 seconds. Add half of the lemon juice and zest along with 1 tablespoon milk and mix until smooth. Add a second cup of confectioners’ sugar, and mix to combine, then add the rest of the lemon juice and zest, and combine. Add the remaining confectioners’ sugar and enough milk to pull the frosting together to be spreadable. Increase the mixer speed to medium-high and mix until fluffy, about 30 seconds.
To assemble the cake, place one cooled cake layer on a cake stand. Spread with about ½ cup of the frosting. Top with about ½ cup of the blueberry preserves. Place the second layer on top. Spread the tops and sides with the remaining frosting. Spoon the remaining (or as much as you like) blueberry preserves over the top. Garnish with fresh blueberries and lemon zest, if desired. Slice and serve.