Cookie dough
1-Adjust the oven rack to the middle: Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line two large baking sheets with parchment/baking paper.
2-You can prepare the cookie dough using: You can prepare the cookie dough using a stand mixer fitted with the paddle attachment, a hand mixer fitted with the double beaters, or by hand.
3-Add the sugar and lemon zest to: Add the sugar and lemon zest to a large bowl (or the bowl of a stand mixer, if using), and use your fingertips to rub the zest into the sugar. Tip: This helps to release more essential oils from the zest, and it’ll make your cookies even more lemony and aromatic.
4-Add the softened butter and vanilla, and: Add the softened butter and vanilla, and cream everything together until pale and fluffy.
5-Add the egg yolks and mix well: Add the egg yolks and mix well to combine.
6-In a separate bowl, whisk together the: In a separate bowl, whisk together the gluten free flour blend, baking powder, xanthan gum and salt, and add them to the wet ingredients.
7-Mix well until you get a smooth: Mix well until you get a smooth cookie dough with no flour clumps. It should have a scoopable consistency and shouldn’t be sticky to the touch.

Marbling the cookie dough with blueberry jam
8-Transfer ⅓ of the cookie dough into: Transfer ⅓ of the cookie dough into a separate large bowl or deep plate and spread it out.
9-Dollop over ⅓ of the blueberry jam: Dollop over ⅓ of the blueberry jam and use the end of a knife or a small offset spatula to swirl it around.
10-Cover the underlying jam-swirled layer with the: Cover the underlying jam-swirled layer with the next ⅓ of the cookie dough. To do this, take small portions of the cookie dough, flatten them with your fingers and lay them on top of the jam-swirled layer until it’s completely covered.
11-Dollop over ⅓ of the blueberry jam: Dollop over ⅓ of the blueberry jam and swirl it around, then use the remaining cookie dough to completely cover the underlying layers.
12-Dollop over the remaining blueberry jam and: Dollop over the remaining blueberry jam and swirl it around.
13-Finally, use a silicone spatula to gently: Finally, use a silicone spatula to gently fold the cookie dough over itself 2-3 times, to ensure even marbling – but don’t overdo it, you don’t want the blueberry jam to get mixed into the cookie dough too much.

Cheesecake filling
14-In a bowl, using a wooden spoon: In a bowl, using a wooden spoon or silicone spatula, mix the room temperature cream cheese and sugar together until well combined and smooth.
15-Add the warm heavy/double cream and the: Add the warm heavy/double cream and the vanilla, and fold everything together into a fairly loose, smooth mixture. It should have the consistency of cheesecake filling, but it shouldn’t be too runny. Tip: If your filling is too firm (especially if you’re using the block-style cream cheese available in the US), you can add a teaspoon or two of extra cream to loosen it up.

Assembling & baking the cookies
16-Put the granulated sugar into a small: Put the granulated sugar into a small bowl.
17-Use a 2-tablespoon cookie or ice cream: Use a 2-tablespoon cookie or ice cream scoop to scoop out a portion of the cookie dough, and drop it directly into the granulated sugar. Roll it around until it’s evenly coated, then roll it between your palms to shape it into a ball. (The sugar coating will allow you to handle the jam-swirled cookie dough without it sticking, so you can roll it between your palms.)
18-Place the sugar-coated cookie dough ball onto: Place the sugar-coated cookie dough ball onto the lined baking sheet, and use a 1-tablespoon measuring spoon to make an indent in the centre. Tip: Because of the jam swirl, it’s possible that you’ll get some cracking around the edges when you press down on the cookie dough ball with the 1-tablespoon measuring spoon. Don’t worry if that happens – the filling won’t leak out and your cookies will still turn out amazing!
19-Repeat with the rest of the cookie: Repeat with the rest of the cookie dough until you get 14 cookies in total. As you’re arranging them on the baking sheets, make sure to space them at least 2 inches (5cm) apart, as they will expand and spread out slightly during baking.
20-Fill the cookies with about 2-3 teaspoons: Fill the cookies with about 2-3 teaspoons of the cheesecake filling. They’ll be full to the brim but don’t worry, the filling won’t overflow. You shouldn’t have any filling left over in the end.
21-Bake the cookies, one baking sheet at: Bake the cookies, one baking sheet at a time, at 350ºF (180ºC) for about 10-12 minutes or until they’ve spread and puffed up slightly, and the cheesecake filling has set. As you’re baking the first batch, keep the other baking sheet at room temperature on your counter – no need to keep it in the fridge.
22-The cookies will be very soft and: The cookies will be very soft and fragile immediately out of the oven. Allow them to cool completely to room temperature on the baking sheet – trying to move them around (for example, to a wire cooling rack) could make them crumble or break. While the cookies are cooling, prepare the blueberry sauce. Tip: If you wish, you can correct the shape of the cookies while they’re still hot and malleable, immediately out of the oven. Just use a round cookie cutter, slightly larger than the cookie diameter, to nudge them into shape.

Blueberry sauce
23-Combine the blueberries, sugar and lemon juice: Combine the blueberries, sugar and lemon juice in a saucepan, and cook them over medium-low heat until the blueberries have released their juices. At this point, the blueberries should be soft but not mushy. Remove from the heat.
24-In a small bowl, mix together the: In a small bowl, mix together the cornstarch (US)/cornflour (UK) and water, then add the cornstarch slurry to the blueberry mixture and stir well to combine.
25-Cook over medium-high heat with constant stirring: Cook over medium-high heat with constant stirring until the blueberry juices have thickened, about 2-3 minutes.
26-Remove from the heat, pour the thickened: Remove from the heat, pour the thickened blueberry sauce into a bowl and allow to cool to room temperature.
27-Just before serving, add a spoonful of: Just before serving, add a spoonful of the blueberry sauce on top of each cookie.

Storage
28-The gluten free blueberry cheesecake cookies keep: The gluten free blueberry cheesecake cookies keep well in a closed, airtight container in the fridge for up to 3 days. Any leftover blueberry sauce can be stored in a closed, airtight container in the fridge for up to 1 week.