For the Caramel Filling:

1. Start by making the caramel filling so it has adequate time to cool before using it to fill the cookies.
2. Set a medium saucepan over medium-high heat. Sprinkle the sugar all over the bottom of the pan. Cook the sugar, stirring constantly, until it melts and turns a light amber color, about 5-7 minutes. Make sure to watch it and stir it the entire time – sugar burns quickly! It will clump up quite a bit before it melts, so don’t be alarmed if it looks crystallized and clumpy before it fully melts. Just keep stirring!
3. Add the cubed butter, a few pieces at a time, and whisk carefully until it is melted and combined. The butter will make the sugar sizzle up a bit, so be careful.
4. Once all the butter is melted and incorporated, carefully pour in the heavy cream. It will splatter so do so very slowly and carefully.
5. Stir to combine and bring the caramel to a boil. Boil for 1 minute.
6. Remove the pot from the heat and stir in the espresso powder, vanilla, and sea salt. Stir well to incorporate.
7. Fully cool the caramel to room temperature. It will get thick and glossy as it cools.

For the Cookie Dough:

1. Combine the softened butter and sugars in the bowl of a stand mixer (you can also mix with a hand mixer in a standard bowl). Beat the butter and sugars together until smooth, creamy, and slightly fluffy, about 5 minutes.
2. Add in the egg yolks and vanilla bean paste and beat to combine.
3. In a mixing bowl, whisk together the flour, espresso powder, cinnamon, cornstarch, and salt until well combined.
4. Add the dry ingredients into the wet and mix until combined. The dough will be thick and crumbly. It should easily hold it’s shape when you press it together..

For Coating the Cookies:

Whisk together the sugar and cinnamon in a shallow bowl until well combined.

Forming the Cookies:

1. Using a 1-tablespoon cookie scoop, scoop out heaping tablespoon balls of the dough, roll them into smooth balls in your hands, and then roll them in the cinnamon sugar to coat.
2. Place the coated cookie dough balls on parchment-lined baking sheets, leaving a couple inches of space in between.
3. Use a ½ teaspoon measuring spoon to gently press an indentation in the center of the cookie dough (you can also use your thumb – the measuring spoon just ensures that the indentations are round and even).
4. Transfer the formed cookies to the freezer for 20 minutes. Preheat the oven to 375°F while the cookies chill.
5. After the cookies have chilled for 20 minutes, transfer them straight to the hot oven. I did mine in two batches.
6. Bake the cookies for 10-12 minutes, or until set and lightly golden brown around the edges.
7. Remove the cookies from the oven and allow them to cool completely on the tray.
8. Once they are cooled, fill the cookies with the caramel sauce, using roughly 1 teaspoon for each cookie. The caramel will be very thick, so I find that using two small spoons to fill the cookies works best.
9. Sprinkle flaky salt over the caramel.
10. Allow them to set completely before storing – for me this took about 30 minutes of sitting at room temperature for the caramel to firm up.