Place a rack in the centre of your oven and preheat oven to 375ºF.
Grease the bottom and sides of a 9-inch pan, I used a square pan but you can use a circular one.
Rinse the raspberries and set aside on paper towels to dry.
In a small bowl, whisk together the flour, baking powder, baking soda and salt. Set aside.
In the bowl of your mixer, combine butter and sugar and beat on medium speed until pale and fluffy, about 3 to 5 minutes.
Add egg, lemon zest and vanilla, beat until combined. With the mixer on low-speed, add the flour mixture in 3 batches, alternating with buttermilk, starting and ending with the flour, and mixing until just combined.
Spread the batter evenly into the pan and arrange the raspberries on top of the cake.
Sprinkle the cake with remaining tablespoon of sugar.
Bake for approximately 18 to 22 minutes, until the top is golden brown and a toothpick inserted in the cake comes out clean.
Remove the cake from the oven, let it cool in the pan on wire rack for 10 minutes and then invert the cake onto a rack to cool completely.
Wait 15 minutes more and then invert cake back onto a plate.
Notes
Store bought or homemade buttermilk will work in this recipe.
Cover leftover cake and store in the refrigerator for up to 4 to 5 days.