In a small pan, bring the milk to the boil then take off the heat and leave to one side. Add the butter to the milk and allow it to melt.
In a jug, mix the yeast with lukewarm water and a teaspoon of sugar. Stir or whisk until dissolved and set to one side. It should begin to bubble.
In a stand mixer or a large bowl, beat the eggs for five minutes until creamy to incorporate lots of air. Add the caster sugar, a pinch of salt and vanilla and mix well. Add the milk and butter mixture, along with the dissolved yeast and mix well. Stir in the flour, raisins and orange and lemon peel and mix to combine.
Cover the bowl with cling-film and leave in a warm place for an hour - first rise.
Preheat the oven to 350F/180C. Grease your cake tin well with plenty of butter.
Carefully pour the dough into the tin, cover again and leave for 30-40 minutes - second rise.
Remove the cling-film and bake in the oven for 30-35 minutes. The Babka should be golden and a cake tester should come out clean.
Leave the Babka to cool in the tin. Once cool enough to handle, transfer it out onto a plate and dust with icing sugar. The Babka will keep well in a tin for up to 2 days.