Preheat the oven to 160° C fan.
Zest the orange & press the juice.
Cream butter & sugar. Add the eggs - all w/ the handheld electric mixer.
Add vanilla extract & salt.
Mix flour & baking powder.
Add the sugar-butter-egg mess & the orange zest as well as the orange juice.
Fill into the paper moulds w/ a spoon.
Bake for about 15-20 min.
Make the famous test w/ the wooden pin ... (after 15 min!).
Let the muffins cool down.