Plum and ginger cobbler

Name: Plum and ginger cobbler
Prep time: 10 min
Cook time: 45 min
Total time: 55 min
Cuisine: European, British
Ingredients: 750g plums, cut into wedges; 4 balls stem ginger in syrup, drained and finely chopped; 1 lemon, juice; 1 orange, zest; 100g light brown muscovado sugar; 125g self-raising flour; 125g self-raising brown flour; 125g unsalted butter, cubed and chilled; ½ tsp ground ginger; 75g walnuts, toasted and roughly chopped; vanilla ice cream, to serve