Start by making the streusel filling. In a medium bowl, mix together the flour, brown sugar, cinnamon, and a pinch of salt. Use your fingers to blend in the softened butter until it resembles small clumps. Pop this in the fridge while you get on with the cookies.

Preheat your oven to 400°F and line two baking sheets with parchment paper or silicone mats.

In a large bowl, stir together the all-purpose flour, cake flour, cornstarch, cinnamon, baking soda, baking powder, and salt. Set this mix aside for now.

Grab a stand mixer and add the cubed butter and both sugars. Mix on medium speed for about 1-2 minutes until it’s all creamy and smooth.

Beat in the egg, egg yolk, and vanilla extract until everything is well combined. If any mixture clings to the sides, use a spatula to scrape it down and mix again.

Slowly add in the dry ingredients, about a quarter cup at a time, mixing until just combined.

Roll the dough into about 8 large balls (or smaller if you like) and place them on your prepared baking sheets.

Make a little indent in each ball using your thumb or the back of a spoon.

Spoon about a tablespoon of the chilled streusel filling into each indent. Bake for around 9-11 minutes, or until the edges look set and slightly golden. Remember, they’ll keep cooking a bit after you take them out, so don’t let them go too long!

If you want perfectly round cookies, as soon as they’re out of the oven, you can gently swirl a larger cookie cutter or glass around them.

Let the cookies cool on the sheet for about 5 minutes before moving them to a cooling rack.

For the icing, whisk together the powdered sugar, melted butter, heavy cream, and vanilla. Once the cookies are cool, drizzle this sweet icing over the tops and enjoy!