Position rack in center of oven, preheat to 350 degrees.
Generously butter an 8.5? x 4.5? loaf pan, and line the bottom with parchment paper.
Sift the flour, baking powder and salt into a medium bowl.
Beat the eggs in a large bowl and add the yogurt, sugar, orange peel, vanilla, butter, orange juice concentrate and the orange liquor. Mix until well blended.
Gradually whisk the dry ingredients into the wet.
Transfer batter to the prepared pan and bake until a tester inserted comes out clean, about 50 minutes.
Cool loaf on rack for 5 minutes. Turn the cake onto the rack and let cool.
In a tiny pot, melt the marmalade with the water. Brush glaze onto loaf and allow to set.
Serve in large pieces–for breakfast, for dessert, for snack, in lunches, and any other time you can think of…