Preheat oven to 350 degrees.

For the filling, toss the rhubarb with sugar, flour and water in a bowl and let sit for about 20 minutes to allow the pieces of rhubarb to get juicy.

To make the crust, whisk hazelnut flour, salt and sugar together in a bowl.

Add wet ingredients and mix well, kneading with your hands until the dough forms a ball.

Refrigerate the dough for about an hour or freeze it for 10 minutes.

Press the dough between two sheets of parchment paper and roll flat to about ⅛-inch thickness.

Cut into circles and pinch into prepared muffin tins. For my average muffin tin size, I use a ring from a wide-mouth Mason jar, which has a 3½-inch diameter. You don’t have to cut circles—you can just pinch the dough into the muffin pans. But cutting circles will make the edges more decorative and consistent.

Spoon the rhubarb mixture into an 8-by 8-inch pan.

Put both dishes into the oven and bake for 8 to 10 minutes, until tarts are golden brown.

Remove the tarts and allow to cool while the rhubarb continues to bake for about 10 more minutes. Remove when it is juicy and tender.

Chill the filling in the fridge until ready to serve, then gently spoon the rhubarb mixture into the tarts until full.

Top each tart with 1 tablespoon mascarpone cheese and 3 raspberries. The easiest way to add the mascarpone is to put it into a baggie, snip the end and pipe it onto the tart. But you can also spoon it on.