Preheat oven to 375°F. Spray a muffin pan with non-stick spray or line with cupcake liners.
Whisk the eggs and sugar. Add in the lemon zest, heavy cream and vegetable oil. Continue to whisk until smooth.
Add the flour, baking powder, vanilla, cornstarch and salt.
Lastly, fold in the blueberries. Let the batter sit at least 10 minutes before baking. (This helps the muffins to have that nice & high, rounded top!) This is a great time to make the crumble!
Prepare the crumble topping by combining cold butter, flour and powdered sugar. Mix with a fork until mixture is uniformly crumbly.
Scoop batter to fill each muffin cup about 2/3 full.
Spoon crumble on top of each muffin, making sure it's completely covered.
Bake muffins for 15-20 minutes at 375 °F. Let cool in pan for 5-7 minutes. Transfer to a cooling rack. Enjoy!