In a small saucepan, heat the orange liqueur. Turn off the heat and add the cranberries, making sure all the cranberries are submerged in the liquid. Set aside.
In a small bowl, mix together the cinnamon and the orange zest. Stir in the flour, baking powder, and salt. Set aside.
In a large bowl, mix together the eggs, butter, sugar, and vanilla. Add the dry ingredients and stir to combine. Add the apples, walnuts, and drained cranberries. Spoon the mixture into a lightly greased 8 by 8 by 2-inch glass baking dish or 8-inch cake pan. Bake until a wooden skewer inserted in the center of the cake comes out clean, about 30 minutes.
To serve, while still warm cut into squares or wedges and serve with ice cream.