Preheat oven to 350°F/175°C. Grease and line a loaf pan.
In the bowl of a stand mixer with the paddle attachment, beat the butter and sugar until fluffy, about 3 minutes. Add the eggs one at a time, mixing well between each addition. Beat in the lemon zest and vanilla extract.
In a medium bowl, whisk together the flour, salt and baking powder. While the mixer is running on a low speed, gradually pour in the dry ingredients, alternating with the milk, ending with the dry.
Add the cranberries and fold them in. Transfer to the loaf pan. Bake for 55-70 minutes. It's ready when a toothpick inserted comes out clean.
Make white chocolate frosting
In a small bowl, break up the white chocolate and microwave in 15 second bursts, stirring in between each burst until the chocolate is melted. You can also put the chocolate in a bowl over a saucepan with an inch of boiling water, stirring util the chocolate is melted.
In the bowl of a stand mixer with the paddle attachment, beat the cream cheese, sour cream and butter together until smooth.
Pour in the melted white chocolate and vanilla and beat until completely combined.
Make the sugared cranberries
In a small saucepan, dissolve 50g of the sugar and water over a medium heat. Using a silicone spatula, you can stir occasionally to help dissolve the sugar. Once all the sugar is dissolved take it off the heat.
Add the cranberries to this syrup and make sure the cranberries are evenly coated. Place a piece of parchment paper on your counter and use a slotted spoon to take the cranberries out and place on the paper. Let them sit for about an hour.
Put the remaining sugar in a medium bowl and add the cranberries, making sure they're all coated.