Grease and line with parchment a 7” cake pan or prepare your muffin tin with muffin cups (you’ll get about 8 muffins) and preheat your oven to 180°C/350°F.
In a medium bowl, whisk together the flour, sugar, cornstarch, baking powder, baking soda and salt.
In a larger bowl, whisk together the pumpkin or squash purée, oil, milk, cinnamon, ginger, nutmeg, apple cider vinegar and vanilla until smooth.
Add the dry ingredients and stir just until a smooth batter forms, avoid overmixing.
Pour the batter into the cake pan or divide it evenly into the muffin cups. Then top with the streusel (you can keep it in larger chunks or crumble it between your fingers for a finer streusel topping).
Bake the cake for 40-50 minutes or the muffins for 25-30 minutes. Or until a toothpick inserted in the center of either comes out clean.
Let the cake cool about 20 minutes before removing from the pan and transferring to a wire rack to cool completely. For the muffins, take them out of the tin after about 5 minutes to transfer to a wire to cool.