Preheat oven to 350. Grease and flour a 9-inch round cake pan with removable bottom. If you have baking spray, I prefer to prep my cake pans with baking spray.

In a large bowl, sift together the flour, baking powder and salt.

Toss in the lemon zest and with your hands, mix it into the flour mixture to release the lemon essence.

In a large bowl with an electric, or stand mixer, beat the sugar and eggs until creamy (about 5 minutes). You could also make the cake by hand. Beat in the oil and buttermilk. Mix well.

Add flour mixture into the wet mixture a half up at a time. If using a mixer, pause to scrape down the sides of the bowl with spatula and mix well after every addition.

Spoon the cake batter into your prepped cake pan.

Top the cake with the plum slices. Push some of them gently into the cake batter.

Sprinkle the turbinado sugar mixed with the cinnamon and thin pats of margarine (or butter) on top of the cake.

If cake is browning, cover with aluminum foil for remainder of baking time.

Remove the cake from the oven. When it's still hot, use a sharp knife to loosen the edges of the cake from the sides of the pan. If you used a springform pan, pop it open carefully and place the cake (with the pan bottom)on a cake rack to cool.

Let the cake cool completely. Once it cools remove the cake pan bottom (or you could leave it on). Best served warm.