Maple syrup and parsnip muffins

100ml maple syrup

175g butter

160g demerara sugar

3 eggs, lightly beaten

250g self-raising flour

2 tsp baking powder, sieved

½ tsp ground cinnamon

1 tsp ground nutmeg

the juice and zest of an orange

250g parsnips, peeled and grated

1 apple, peeled, cored and grated

20g oats

30g walnuts, chopped