Line the cupcake tin with cupcake cases then set it aside. Preheat the oven to 180C/350F whilst preparing the cupcake mixture.
Melt the white chocolate in a small bowl. I do this in the microwave in short bursts, stirring in between each heating until smooth. Set the melted white chocolate aside to cool slightly. Separately in a jug, mix together the eggs and yogurt.
In a large mixing bowl, cream together the butter and sugar until fluffy. Sift in the flour, baking powder, bicarbonate of soda (baking soda) and salt, beating until the mixture resembles damp sand.
Add ¾ of the wet mixture into the dry and mix to combine. The mixture will be thick. Tip in the remaining wet ingredients and beat until completely mixed in. Pour in the cooled white chocolate and beat to combine all the ingredients until smooth. Turn the mixer speed to high and beat for 30 seconds until really pale and fluffy.
Spoon or scoop the cupcake mixture evenly between the cases, filling no more than halfway full, then bake in the preheated oven for 20-22 minutes until springy to touch and a wooden skewer or toothpick inserted into a cupcake comes out clean. Leave them to cool for ten minutes in the tin, then remove the Christmas tree cupcakes to a cooling rack and allow them to cool completely.