Preheat the oven to 325°F/160°C.
Grease and flour two medium loaf pans or 1 10-in. tube pan/bundt pan.
Separate eggs into yolks and whites. Beat the yolks. Cream the butter with the sugar and mix in yolks.
Sift the flour and the baking soda together. Alternately add the flour and yogurt to the creamed sugar. Stir in the lemon zest and extract.
In a separate bowl, beat the egg whites until they hold stiff peaks. Fold the egg whites into the batter and mix thoroughly.
Pour the batter into the prepared loaf pans and bake for 1.5 hours or until a cake tester inserted into the center of the loaf comes out clean.
Mix the ingredients for the glaze and spread over the warm cake(s). Most of the glaze will be absorbed.