In a medium bowl, whisk together the flour, sugar, and salt.

Cut in the cold butter until the mixture resembles coarse breadcrumbs.

Use your hands to work the dough a bit and to bring the dough together. The dough should be crumbly but cohesive when squeezed. It won’t form a ball or a loose ball like with pie dough.

I placed a piece of plastic wrap in a mixing bowl and then dumped the dough into there and wrapped it up into a very loose, crumbly disc.

Chill for 1 hour or up to 3 days.

Grease 4 mini tart pans with removable bottoms.

Take a fourth of the dough crumbles (I used 91 grams, but I used the extra tablespoon of milk - if you follow the recipe exactly, you can use 88 grams) and place in the pan.

Press up the sides and evenly over the bottom of the pan. Do the same with the other 3 tart pans.

Place in the fridge for at least 30 minutes or cover and refrigerate for up to 3 days.

Towards the end of the chill time, preheat the oven to 375 °F (190 °C) and place a baking sheet large enough to fit all 4 tartlets in the lower third of your oven.

After 30 minutes of chilling, place the tartlets directly onto the hot baking sheet and bake for 18-22 minutes, rotating halfway through if you notice them browning too quickly in certain areas, until the sides are nicely browned and the bottom has browned a bit.

Remove the baking sheet and tartlets from the oven and place them on a wire rack to cool completely, about 1 hour (get started on Step 15 during this time). The crusts will crumble if you try to remove them from their pans while still warm. If making ahead of time, you can put the cooled crusts in an airtight container and store at room temp for up to 3 days or refrigerate for 5 days.

Once cooled, unmold the crust - the removable bottom is going to stick to the bottom for now, and that’s okay.

After about 40 minutes of cooling (or sooner if they cool more quickly in your kitchen), start the filling.

In a 1-quart (1-liter) saucepan, add 1 1/2 cups (225 grams) of blueberries, 1/3 cup (80 ml) water if using granulated sugar or 1/4 cup (120 ml) water if using maple syrup, granulated sugar and salt.

Bring to a simmer over medium-high heat while stirring occasionally. When it’s almost simmering, mix together the cornstarch and water in a small bowl.

Once the blueberries start simmering, stir in the cornstarch slurry.

Turn the heat down to low and let it cook until it’s thickened - anywhere from 20-60 seconds. You don’t want it gloopy or too runny.

Remove from the heat and stir in the almond and vanilla extracts.

Let the sauce cool for about 10 minutes. It can be warm, but not steaming hot.

Divide the filling between each cooled crust. Use 5 tablespoons (82 grams) per tart, and if there’s any left, add it. The exact amount the filling yields depends on your blueberries and exactly how thick the sauce is - I got different amounts every time, but always had at least 5 tbsp worth per tart.

If you chill the filled tarts for 4+ hours and let the filling soak in a bit, then you'll be able to easily remove the tart pan's removable bottom from the tartlet. I think they're most delicious after they've chilled for 4+ hours or the next day.

Once you've filled the tarts, they can be refrigerated for up to 3 days. You can freeze the unbaked or baked tart shells, but not the filling.