Vegan Blueberry Muffins with Streusel Topping

Preheat your oven to 190°C (fan) / 375°F / Gas Mark 5. Line a muffin tin with paper cases.
Toss the frozen blueberries in a teaspoon of flour, then return them to the freezer until needed.
Make the streusel topping, by whizzing together all the ingredients in a mini-chopper, (or rubbing the margarine into the flour by hand, then adding the sugar). Set aside until needed.
Blitz the fresh blueberries to a pulp, or mash them with a fork. Tip into a food mixer or large bowl, and beat in the margarine and sugar until light and fluffy.
Sift in half of the flour and half of the yoghurt and mix well, then slowly fold in the remaining flour and yoghurt and add the bicarbonate of soda and salt. Mix until just combined and no lumps remain, don't over-mix.
Divide the mixture between the muffin cases, then divide the frozen blueberries between the muffins, placing them on top and gently pressing down. Finally, top each muffin with a sprinkle of streusel topping.
Bash the muffin tin onto your work surface (to remove bubbles that will have started to form), then bake the muffins for 25-30 minutes until an inserted knife comes out clean. Enjoy warm from the oven, or keep in an airtight container.