1.Preheat oven to 220°C (200°C fan-forced). Oil 19cm x 29cm slice pan.
2.Beat butter, sifted icing sugar and yolks in small bowl with electric mixer until light and fluffy. Transfer mixture to large bowl; stir in mashed potato.
3.Add sifted dry ingredients; stir to make a soft dough. Knead dough lightly on floured surface until smooth. Roll dough between sheets of baking paper to 20cm x 30cm rectangle.
4.Spread tomato paste over dough; sprinkle with ham, spinach and 1 cup of the cheese.
5.Starting from long side, roll dough firmly using paper as a guide; trim ends. Cut roll into 12 slices; place pinwheels, cut-side up, in single layer, in pan.
6.Bake 20 minutes. Remove pinwheels from oven, sprinkle with remaining cheese; bake a further 10 minutes.
Helpful hint Pizza cheese is a commercial blend of processed grated mozzarella, parmesan and cheddar cheeses. Use plain cheddar cheese if you like, or use a tasty or mature cheddar for extra bite.Note