Position your rack inside your oven to the middle level and preheat to 350 degrees.
Combine together the flour, baking powder and salt. Set aside. (if using cake flour, this is usually already sifted so you don't have to do anything but if using all-purpose flour, please sift)
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed until creamy and smooth, about 30 seconds. Add the granulated sugar and continue beating until light and fluffy, about 4-5 minutes. Stop the mixer occasionally to scrape down the sides of the bowl. Add the eggs one at a time, beating well after each addition. Beat in the vanilla until well incorporated, about 1 minute.
Reduce the speed to low and add the flour mixture in three additions, alternating with the milk and beginning and ending with the flour. Beat each addition until just incorporated, again, stopping the mixer occasionally to scrape down the sides of the bowl.
Pour the cake batter into your cake pan. Bake until the cake is lightly golden and slightly firm, for about 40 minutes. DO NOT OVERCOOK. When finished, transfer the pan to a wooden cutting board or other safe, cooling surface and let cool for about 10-12 minutes.
Once completely cooled, release the cake from the cake pan and even out your cakes, ie: you will most likely have to even out the cake and slice off the portion that is uneven. Flip the first cake onto your cake plate or cake stand. You want the bottom of the cakes on top since they are flatter.
Spread the raspberry jam over the bottom layer cake. Flip the second cake (bottom side up) on top.