To prepare the crust, mix together the dry ingredients in a large bowl. Grate the frozen butter over the bowl on the largest hole setting, stopping every couple minutes to stir in the grated butter bits so that they don’t form one giant butter shard clump. Add the water in small increments, stirring, until all the water is added. Knead the dough for about 30 seconds to help disperse the moisture, then grab a handful of the mixture and squeeze. If it generally sticks together when you let go, it is fine. If it completely crumbles apart, it needs another tablespoon or two of water. Once the dough holds its shape, divide it into two balls, cover each with plastic wrap and place them the refrigerator.
For the white chocolate mascarpone topping, heat the mascarpone in a small saucepan over low heat, stirring every minute or two, until the mascarpone melts down to a hot but not boiling liquid. Remove from heat and set aside. In the top of a double boiler, melt the white chocolate chips until smooth, stirring constantly. Working quickly, remove the top from the double boiler, wiping any excess moisture from the bottom with a towel, and drizzle the melted white chocolate into the hot mascarpone in a thin and steady stream while whisking the mascarpone mixture constantly until all of the white chocolate has been incorporated.
Continue whisking gently for 5 more minutes to help it cool. Set it aside and allow it to cool to room temperature and solidify as you finish the pie. Preheat the oven to 375 degrees Fahrenheit.
For the filling, whisk together the golden syrup, flour, sugar, cinnamon, cloves, and salt in a medium bowl. Add the fruit and toss to coat. Set aside. Roll out one of the dough balls on a clean working surface until it is about 1/8 inch thick. Transfer it to an 8-inch pie dish and press it into the pan, leaving the sides overhanging.
Now roll out the second dough ball into a circle. This will make the lattice top. Cut the rectangle into 30 long strips using a pizza or pastry wheel. Braid three strips together, and repeat until you have 10 separate braids. Pour the filling into the pie crust shell. Weave a lattice pattern using your braids, with five going vertically and five going horizontally. Trim the edges of excess crust overhand and place the pie in the oven. Bake until golden on top and filling is soften, about 1 hour. Remove and allow to cool for 30 minutes before slicing and serving alongside the white chocolate mascarpone.