Preheat the oven to 400°F (200°C) and measure out the muffin ingredients. Line a 12-cup muffin pan with liners and spray them with cooking oil.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.
In a separate bowl, mix the oil, egg, and milk. Gradually add the dry ingredients, one-third at a time, mixing until everything is just combined.
Gently fold in the blueberries. Use a dough scoop to fill each muffin cup about ¾ full for even-sized muffins.
In a small bowl, combine the sugar, flour, butter, and cinnamon with a fork to make the crumb topping. Sprinkle over each muffin.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean. Cool in the pan for 5 minutes, then transfer to a rack to cool completely.
Heat the heavy cream in a saucepan over medium heat until just before boiling. Remove from heat and stir in the white chocolate chips until smooth and creamy.
Let the ganache cool until thickened, then drizzle it over the muffins with a spoon or squeeze bottle.
Once the ganache sets, garnish with fresh blueberries and enjoy!
Notes
Storing Blueberry MuffinsTo store blueberry muffins: first, transfer them to an airtight container lined with paper towels. Cover the muffins with another paper towel or two and seal the lid. The paper towels will work to absorb any moisture put off from the muffins. Store the muffins at room temperature for up to 2 days. Always label the date on the outside of the container to keep up with freshness.