Step 1: Brine the Lemons (Optional, but Recommended). In a small bowl, combine the dill pickle brine and water. Place the whole lemons in the brine, making sure they’re submerged. Let them sit at room temperature for at least 30 minutes, or refrigerate for up to a few hours. This will infuse the zest with a subtle pickle flavor.

Step 2: Preheat Oven and Prepare Pans. For the cake: Preheat the oven to 350°F (175°C). Spray two 8-inch round cake pans with baking spray with flour. (Alternatively, butter and flour the pans.) Line the bottoms of the pans with parchment paper circles and spray (or butter) again.  

Step 3: Whisk Dry Ingredients. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

Step 4: Whisk Wet Ingredients. In a large bowl, whisk together the granulated sugar, melted butter, vegetable oil, and lemon zest (zest the brined lemons after removing them from the brine and drying them) until combined.

Step 5: Add Eggs. Whisk in the eggs, one at a time, until lightened in color, about 1 minute.

Step 6: Add Buttermilk, Lemon Juice, and Vanilla. Whisk in the buttermilk, lemon juice, and vanilla extract.

Step 7: Combine Wet and Dry Ingredients. Add the flour mixture in 3 parts, whisking to combine after each addition.

Step 8: Divide Batter and Bake. Evenly divide the batter between the prepared pans. Tap the pans a few times on a kitchen towel on your countertop to level the surface and remove air bubbles. Bake until a toothpick inserted in the center comes out with only a few crumbs, 30 to 35 minutes.  

Step 9: Cool Cake Layers. Transfer to a cooling rack. Let cool in the pans for 10 minutes, then turn out onto a cooling rack to cool completely, about 1 ½ hours.  

Step 10: Make the Jam Filling (While Cake Bakes/Cools). Meanwhile, in a small bowl, whisk together the cornstarch and 1 tablespoon of water. In a small saucepan, heat the jam over medium heat until pourable and smooth, about 1 minute.

Step 11: Thicken the Jam. Remove the jam from the heat and whisk in the cornstarch mixture. Return the saucepan to medium heat and bring the mixture to a boil. Boil, stirring constantly, until no longer cloudy with cornstarch and a rubber spatula dragged through the mixture reveals the bottom of the pan for a few seconds before the jam flows back together, 2 to 3 minutes.

Step 12: Cool the Jam. Transfer the thickened mixture to a bowl and let it cool completely.

Step 13: Make the Frosting. To the bowl of a stand mixer fitted with the paddle attachment, add the butter. Beat on medium speed until smooth, about 1 minute. Scrape down the bottom and sides of the bowl.  

Step 14: Add Jam, Lemon Juice, and Vanilla. Add the jam, lemon juice, vanilla extract, and dill pickle powder, and beat on low speed until just combined, 30 seconds. The mixture might appear broken, but that is okay.

Step 15: Beat Until Smooth. Increase the speed to medium and beat until the butter and jam are no longer separated, 1 to 2 minutes.

Step 16: Gradually Add Powdered Sugar. Gradually add the powdered sugar and beat on low speed until combined. Scrape the bottom and sides of the bowl.

Step 17: Beat Until Fluffy. Increase the speed to medium and beat until smooth and fluffy, 3 to 4 minutes.

Step 18: Assemble the Cake. Place one cake layer on a cake plate. Spread about ½ cup of frosting over the top; this will be a barrier to prevent the cake from absorbing the jam filling.  

Step 19: Pipe a Frosting Border (Optional). Spoon about ½ cup of the frosting into a zip-top bag and cut a ¾-inch opening in one corner. Alternatively, use a pastry bag fitted with a ¾-inch tip. Pipe a thick border around the edge of the frosted cake layer; this will prevent the jam filling from leaking out the sides of the cake.

Step 20: Add Jam Filling. Stir the jam filling to loosen it up. Spread the filling on top of the cake within the frosting border, leaving about ½ inch of space between the filling and the border.  

Step 21: Top with Second Cake Layer. Top with the second cake layer.

Step 22: Crumb Coat. Spread about 1 cup of frosting in a thin layer over the top and sides of the cake. This is called a “crumb coat” and it helps to seal in any loose crumbs.

Step 23: Chill. Chill the cake, uncovered, in the refrigerator for 30 minutes or in the freezer for 10 minutes to set the frosting and the filling.  

Step 24: Frost the Cake. Use the remaining frosting to frost the top and sides of the cake.

Step 25: Decorate and Serve. Decorate the cake with the raspberries and fresh dill (optional). Serve.