Preheat oven to 350 degrees F. Grease and flour a 9x13-inch cake pan, set aside.

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

In the bowl of a stand mixer, cream together the butter, sugar and lemon zest on high until light and fluffy, about 3 minutes. Stir in the oil and then add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract. In a measuring cup, stir together the lemon juice and buttermilk. Add the dry ingredients and buttermilk, alternating between the two, starting and ending with the dry ingredients and mixing just until combined after each addition. Pour the batter into the prepared cake pan and spread out evenly. Bake until a toothpick inserted in the middle comes out clean, about 35 to 40 minutes. Remove from the oven and let cool completely.

To make the the butter cream, blend the thawed raspberries until smooth, and then strain out the seeds using a fine mesh strainer. Set aside. Cream together the butter and 3 cups of powdered sugar until fluffy. Stir in the vanilla and salt. Add the strained raspberry puree and blend until well incorporated. Add the remaining cup of powdered sugar and beat on high for 3 minutes.

Invert the cooled cake onto a large cutting board. Using a serrated knife, cut the cake in half, so you end up with two thin layers. Place on layer on a baking sheet or large platter. Spread the cake with the raspberry jam and then place the second layer of cake on top. Frost the top of the cake with the buttercream and sprinkle with poppy seeds. Cut into thin pieces and enjoy. Leftovers can be stored in the fridge, wrapped in plastic wrap, for up to 3 days. Just let come to room temperature before serving.