How to Make It
Place currants and wine in a small bowl, and set aside.
Melt butter in a large skillet over medium. Using a silicone spatula, fold in leeks until coated. Cook, stirring often, until leeks are wilted to half their original volume, about 5 minutes. Fold in kale and celery, and season with salt. Continue cooking until vegetables are tender, about 10 minutes. Stir in thyme, rosemary, sage, currants, and wine. Increase heat to high, and cook until all liquid is evaporated, about 4 minutes. Remove from heat, stir in zest, and let cool before using.