Preheat your oven to 220°C (425°F) and prepare a jumbo 6-cavity muffin pan with muffin liners or grease it generously with melted vegan butter.

In a small bowl, combine the flour, sugar, melted butter, and cinnamon, mixing until well blended. The crumble may be soft but will firm up once chilled. Place it in the freezer until you're ready to use it.

If desired, mix the sugar and lemon zest in a large mixing bowl, rubbing them together with your fingertips until fragrant.

Add the remaining dry ingredients to the bowl and mix thoroughly.

Incorporate all the wet ingredients, except for the blueberries, and stir until just combined.

Gently fold in the blueberries until evenly distributed.

Spoon the batter into the muffin cups, filling each one nearly to the top.

If using, add about 2 teaspoons of blueberry preserves on top of each muffin and spread it across the surface. Then, sprinkle the crumble topping over each muffin.

Bake the muffins at 220°C (425°F) for 5 minutes. Without opening the oven, reduce the temperature to 180°C (350°F) and continue baking for an additional 28-32 minutes.

The muffins are done when the tops are lightly golden and the crumble appears dry. A toothpick inserted in the center should come out clean, though a few moist crumbs or jammy bits are acceptable.

If you skip the jam topping or crumble, reduce the baking time by 5 minutes.

Allow the muffins to cool in the pan for 10 minutes before transferring them to a wire rack.

Enjoy the muffins warm or at room temperature! Store them in an airtight container at room temperature for up to 2 days, in the fridge for 3 days, or freeze for up to 1 month. Note that the crumble topping will soften after 1 day.