Preheat oven to 350 degrees F. Line a large baking sheet with parchment paper.
In a mixing bowl, whisk together the flour, baking powder, salt, sugar and poppyseeds. If you are using turmeric, add a pinch of that as well.
In a second bowl, whisk together sourdough, egg, oil, lemon zest and lemon extract. Stir sourdough mixture into the flour mixture.
Knead together until you have a firm dough. Divide dough in half and shape into two logs about 6 inches long by 2 ½ inches wide. Do this directly on the baking sheet.
Bake for about 22 to 25 minutes, then remove from oven and allow the biscotti to cool for about 5 minutes or just until it is cool enough to handle.
Meanwhile, reduce oven heat to 300 degrees F.
Cut each log crosswise to make ¾ inch thick slices.
Stand the slices on the baking sheet (or lay them, if you’d prefer) and bake at 300 degrees for about 25 minutes. Transfer to a wire rack and let cool completely.
For a white chocolate dipped version, melt whatever kind of white chocolate you have in the microwave using 50% power and stirring every 40 to 60 seconds. Dip the biscotti in the white chocolate and chill until set.