In a stand mixer fitted with the paddle attachment, cream the butter on medium-high speed until creamy and smooth, about 1 minute.

Turn the mixer speed to medium; add the oil, sugar, and vanilla to the butter; and beat for about 5 minutes, until the mixture is light in color and about double in volume.

Turn the speed to medium-low and add the eggs and egg yolks, one at a time, mixing each until incorporated before adding the next. Scrape the bowl after each addition.

In a medium bowl, whisk together the flour, baking powder, and salt until well combined. In a liquid measuring cup, whisk together the milk and sour cream.

Add one-third of the flour mixture to the butter mixture and mix until combined. Scrape the bowl and add half of the milk mixture, mixing until combined. Repeat with another one-third flour, the remaining milk mixture, and then finish with the final one-third flour, scraping the bowl and paddle after each addition.

Pour the batter into the prepared pan and spread evenly using an offset spatula. Gently tap the pan on the counter several times to release excess air bubbles.

Bake until a tester comes out clean, 25 to 30 minutes. Let the cake cool completely before layering it with the lemon curd and whipped cream.

In a medium stainless-steel bowl, whisk together the egg yolks, sugar, lemon juice, lemon zest, butter and salt.

Put 1 inch of water in the bottom of a double boiler or a medium saucepan and bring to a gentle simmer over medium heat. Place the bowl with the lemon mixture over the simmering water.

Using a rubber spatula, stir the mixture constantly, making sure to clean the sides of the bowl as you go, until the lemon curd begins to thicken, about 10 minutes; it will be the consistency of smooth pudding.

If there are any lumps in the curd, strain it through a fine-mesh sieve into a shallow container and cover with plastic wrap, pressed directly onto the surface, to prevent a skin from forming.

In a large bowl, add enough ice cubes and cold water to create a bath for the container to sit in without the water breaching the sides.

Set the container in the ice bath or place in the freezer until chilled, about 15 minutes, then transfer to the fridge for up to 5 days.

In a stand mixer fitted with the whisk attachment, combine the cream, confectioners' sugar, and vanilla and beat on medium speed until just thick—it will start to leave marks from the whisk in the cream.

Remove the bowl from the mixer and, using the whisk attachment, continue whipping by hand for several seconds until the cream reaches the desired consistency. This ensures the stand won't over-mix.

Whipped cream is best used immediately!

Spread lemon curd over the cooled cake. Top with whipped cream and blueberries. Spoon into bowls or glasses to serve.