In a large mixing bowl, use handheld electric beaters to beat the butter & ricotta together until light and fluffy, 2-3 minutes.

Add flour and salt and mix well. Dough will be dry.

Slowly drizzle on some of the water and beat again. Only add enough water to make a cohesive dough.

Turn out the dough onto a lightly floured work surface. Form the dough into a disk and wrap with plastic wrap.

Place in the fridge and chill for 3 hours to overnight.

While the dough is chilling, make the prune jam.

Place the prunes in a small saucepan and cover them with water. Add sugar and lemon juice.

Bring the pan to a simmer over medium heat and continue to simmer until the mixture has reduced significantly and has a "jammy" texture. Stir occasionally with a spatula, and I also occasionally break up some larger prune chunks with a fork.

When the prune jam is thick and jammy, remove from the heat and set aside to cool until ready to use. If you don't plan to use soon, cover and place in the fridge. The jam can be used in the tarts straight from the fridge if you like.

When you're ready to use the dough, remove it from the fridge. If it's too cold to roll out immediately, let it sit at room temperature for 20-30 minutes before using.

Preheat the oven to 400 degrees Farenheit. Cover baking sheets with parchment paper and set aside.

Lightly flour a work surface and set the dough on it. Roll it out about 1/4 inch thick. 12 inches by 24 inches is a good size to aim for.

Use a pizza cutter or a knife to cut the dough into 3 inch squares (if you have a 12 x 24 rectangle, cut it into 4 squares x 8 squares for 32 tarts total).

Alternatively, you can divide the dough in half and only work with one half at a time!

Make four 3/4 inch cuts in each square. Each cut should be a diagonal, beginning at one corner of the square, toward the middle.

Scoop 1/2 tsp of prune jam into the center of a tart. Choose one cut corner and fold it into the middle of the tart (over the jam). Fold every other corner in so that they meet in the middle, forming the star shape. Transfer the tart to a prepared baking sheet.

Repeat with the remaining tarts.

If desired, beat together the egg and milk with a fork in a small bowl. Use a pastry brush to spread the egg wash onto the tarts.

Bake for 8-11 minutes, until golden.

Allow to cool on the baking sheet for 5 minutes, and then transfer to a cooling rack.

You may want to put parchment paper or something similar under your cooling rack before adding the powdered sugar!

When the tarts are lightly cooled, dust with powdered sugar. I use a small wire strainer to lightly and evenly dust the tarts.

These are definitely best the day they are baked. If you will not eat them all, you may wish to freeze them, then thaw and re-dust with sugar when you're ready to eat them.

You can keep these sealed in a container or bag at room temp for a few days, but they will lose some of their crisp.