Preheat your oven to 350F, or about 175C.
For the topping, add the cold butter, brown sugar, all-purpose flour, rolled oats, Kosher salt, ground cinnamon, and vanilla extract to a medium-sized mixing bowl.
Use your fingers to pinch the cold butter into the remaining ingredients, until you have pieces of butter covered in the other ingredients that are roughly the size of a pea.
Set this crumble topping mixture aside for later.
When you are ready to make the blueberry filling, use some softened butter to lightly grease the insides of two 10-oz ramekins.
Place the ramekins on a sheet tray lined with parchment paper.
*This is just in case some of the juices leak out from the blueberry cobblers as the bake in the oven.
In a medium-sized mixing bowl, combine the blueberries, white granulated sugar, corn starch, lemon zest, and lemon juice.
Mix to combine.
Divide the blueberry mixture between the two ramekins that you greased earlier.
Top each ramekin with half of the crumble topping mixture.
Bake at 350F for roughly 25-30 minutes.
Remove the ramekins from the oven, and allow them to cool down for roughly 10-12 minutes at room temperature.
Serve while the blueberry cobbler is still hot, and top each one with a big scoop of French vanilla ice cream.