Preheat the oven to 350°F/177°C.

Butter a baking dish that can hold 6 cups. It can be a square 8x8, a round 8x2, or some other shape. I used a vintage rectangular pan that happened to be in circulation at the time I was making this cake.

Whisk the flour, baking powder and salt together in a small bowl and set them aside.

In a large bowl using an electric hand mixer, whip the butter and sugar together for 3-4 minutes. You want it to become really light and fluffy. Add the eggs and vanilla extract and mix to combine.

Add the dry ingredients to the wet and mix on the slowest setting, just until everything is uniformly combined.

Scrape the batter into the prepared pan and bake for 18-20 minutes, until a toothpick inserted into the center of the cake comes out mostly clean (a couple dry crumbs are okay).

Let the cake cool for a few minutes and then top with the jam. You want it to be warm so that it absorbs the flavors a bit, but not so hot that the jam liquifies.

Serve warm or at room temperature.