Preheat oven to 350°. Spray a 10-inch cast-iron skillet with baking spray with flour.
For cake: In a medium bowl, whisk together flour, baking powder, salt, cinnamon, ginger, and nutmeg. In a large bowl, whisk together sugar, melted butter, eggs, and cane syrup. Gradually stir flour mixture into sugar mixture alternately with buttermilk, beginning and ending with flour mixture. Spread batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, about 40 minutes. Let cool in pan on a wire rack for 15 minutes. Remove from pan, and let cool slightly on a wire rack.
For topping: In a small bowl, whisk together yogurt, honey, vanilla, and salt until smooth; spread onto warm cake. Drizzle with cane syrup, if desired.
Recipe by Southern Cast Iron at https://southerncastiron.com/gateau-de-sirop/