Make the syrup: In a small saucepan, combine honey and water, and heat over medium heat until the honey dissolves. Bring to a boil. Reduce heat, and simmer for 10 minutes. Remove from heat and stir in liqueur.
Brush a 9-inch tube pan with melted butter and dust with flour. Set aside.
Beat eggs until light and fluffy, add sugar, remaining melted butter, and orange rind and mix until creamy. Combine the flour, baking powder and walnuts in a large bowl. Add the egg and sugar mixture to the bowl and beat thoroughly. Fold in the yogurt. Pour the batter into the prepared pan and bake in a preheated oven at 350ºF for 45-50 minutes or until a cake taster comes out clean. Remove cake from oven and cool on a rack for 5 minutes. Spoon the cooled syrup over the cake and let it stand for at least 3 hours before serving.
