1. Generously butter 10-inch diameter cake pan with high sides (or 7 1/2 x 11 1/2-inch ovenproof glass baking dish).
2. Heat syrup,1/4 cup butter,brown sugar and mace in medium saucepan over low heat, stirring until sugar disolves;bring to boil.
3. Pour into prepared pan and sprinkle with pecans.
4. Position rack in center of oven and preheat to 350 degrees.
5. Sift flour,baking soda and salt into bowl.
6. Using electric mixer, cream 1/2 cup butter in another bowl.
7. Add 3/4 cup sugar and beat until light and fluffy.
8. Beat in eggs, one at a time, then beat 2 minutes;blend in vanilla and lemon peel.
9. Stir in flour mixture and yogurt alternately, beginning and ending with flour mixture; fold in currants.
10. Spoon batter atop pecan mixture, spreading gently to sides of pan.
11. Bake until tester inserted in center comes out clean, about 55 minutes.
12. Immediately invert cake onto rack set over sheet of waxed paper.
13. Serve warm; top with whipped cream if desired.