Heat the butter and milk in a small bowl until the butter is completely melted.

While the butter mixture is still hot, add the semi-sweet chocolate and stir until completely smooth. Cover with lid or plastic wrap and refrigerate to harden until moldable (about 10-15 minutes).

Preheat your oven to 400°F and while the lava filling sets, start making the cookie dough. Add the all-purpose flour, cake flour, cocoa powder, baking soda, salt & cornstarch to a bowl and stir to evenly distribute all the ingredients.

In a large microwave-safe bowl heat the butter until completely melted then add the granulated and brown sugars and mix until smooth. Try to dissolve the sugar as much as possible at this point as this is what will give the cookies that iconic shiny & crackly top like brownies.

Add the vanilla extract and the egg and mix again until the sugar again dissolves as much as possible. A little undissolved sugar is fine.

Add the dry ingredients from earlier and fold in only until there are no more dry spots. Be careful not to over mix.

Allow the cookie dough to chill in the refrigerator for 5-10 minutes.

Assemble the cookies by portioning the cookie dough into 8 equally-sized balls. Take a cookie dough ball in a gloved hand & flatten it. Place the lava filling balls in the center then start to fold the the dough over the filling then roll lightly between your palms ensuring the lava center is completely covered.

Arrange the assembled chocolate lava cookies on a cookie sheet lined with parchment paper allowing for at least 2 inches of space around each.

Bake the cookies for exactly 9 minutes at 400°F on the middle rack of your oven.

Allow to cool slightly but serve warm for the best oozy molten chocolate center. Enjoy plain or dust lightly with confectioner's/icing sugar!

Store in an air-tight container for up to 5 days for optimal taste and texture!