Oaty plum gingerbread slice

Name: Oaty plum gingerbread slice
Ingredients: 140g unsalted butter, plus extra for greasing; 100g dark soft brown sugar; 100g golden syrup; 6 small plums (about 250g prepared weight); 140g plain flour; 1 tsp baking powder; 1 tbsp ground ginger; 1 heaped tbsp chopped stem ginger; 85g porridge oat (not jumbo); 2 large eggs, beaten, at room temperature; 25g plain flour; 25g porridge oat; 2 heaped tsp chopped ginger