Mandarin Orange Cranberry Muffins

1. Preheat oven to 375ºF. Coarsely chop cranberries and mix with 1/4 cup sugar. Set aside.
2. Place streusel ingredients into a small bowl and combine with a pastry blender or to knives until mixture is crumbly.
3. Line a muffin tray. In a bowl combine flour, remaining 1/2 cup sugar, baking powder and soda, salt and vanilla.
4. In another bowl, beat the egg and add Mandarin orange zest, juice and melted butter.
5. Add dry mixture to wet ingredients and stir until just combined. Mix in cranberries and optional nuts.
6. Fill 12 muffin liners with the batter, sprinkle streusel crumbles on top and bake for 15-20 minutes until muffins are golden brown.