Preheat oven to 350 degrees. Butter a 10-inch springform pan or pie plate. Sift flour, baking powder, and salt together into a medium bowl. Set aside.
Put butter and 1 cup sugar in the bowl of an electric mixer fitted with the paddle attachment. Mix until pale and fluffy, about 3 minutes. Add in egg, buttermilk, and vanilla extract. Mix until combined.
Gradually mix in flour mixture. Transfer batter to prepared pan. Arrange strawberry slices on top of batter. Sprinkle turbinado sugar over berries.
Bake cake for 10 minutes at 350 degrees. Reduce oven temperature to 325 degrees. Bake until cake is golden brown and firm to the touch, about 50-55 minutes. Let cool in pan. To serve, cut into wedges. Store cake at room temperature, for up to two days.