Preheat the oven to 350F.
Line a 9x5 inch loaf pan with parchment paper, leaving some overhang so you can lift the finished cake out easily.
Whisk the flour, baking powder, salt, turmeric, and pepper in a bowl.
In a large bowl, combine the one cup of sugar with the lemon zest until the sugar is moistened and pale yellow.
Whisk in the sour cream or yogurt, eggs, melted butter, and lemon juice until well combined.
Mix the wet ingredients into the dry ingredients until well combined.
Pour the batter into the prepared loaf pan, smoothing out the top.
Add the lemon slices and sprinkle the tablespoon of sugar evenly over the top.
Bake for 50-60 minutes, or until the cake is golden brown and a toothpick comes out clean.
Let cool and enjoy!