Preheat the oven to 180C/350F.
Grease the bundt pan with butter.
Mix flour, baking powder and salt well. If you are using dried yuzu powder then mix it with juice.
In the Thermomix bowl place the butterfly whisk and add room temperature butter and sugar. Cream it on speed 3 for 2 minutes.
Remove the butterfly whisk and add in egg, yuzu extract, saffron, buttermilk and flour, mix on speed 5 for 20-30 seconds.
Pour the batter in the greased pan and bake it in the preheated oven for 30-35 minutes or till a toothpick inserted in the centre comes out clean.
After baking let is stand for 5-7 minutes and then cool it on a wire rack.
Serve with tea or coffee.
You can also dress this cake with lemon sugar glaze.