Step 1

In a stand mixer fitted with a paddle attachment, mix the butter on medium/medium-high until broken down and smooth. Next, add the powdered sugar, nut flour, salt, and vanilla and mix until just combined. Add in the egg and mix.

Step 2

Working in two batches, add the flour. Mix until a dough just begins to form (careful not to overmix).

Step 3

Transfer dough to a sheet of plastic wrap and form into a flat disc. Wrap in plastic and store in the fridge for at least one hour (or up to overnight).

Step 4

Preheat oven to 320℉.

Step 5

Unwrap the refrigerated dough. Dust a pastry board or marble slab with flour (reserving a few tbsp extra of flour in case dough sticks too much) and place dough on top. Lightly sprinkle the top of the dough disc with flour and using a rolling pin, roll out the dough until it's about 1/4 inch thick. Gently pick the dough up and place in tart pan. Work gently to press the sides of the dough against the tart pan.

Step 6

Place a piece of parchment paper on top of the tart pan and fill it with dry beans or lentils or with baking weights if you have them. Next, place in oven for 25 minutes.

Step 7

After 25 minutes, remove the tart pan and remove the parchment paper with weights. Mix the remaining egg with heavy cream and using a pastry brush, paint a thin layer of the egg cream mixture over the entire tart, including the tops of the sides. This will help prevent the tart from turning too brown during the next bakes.

Step 8

Place in oven for 10 minutes.

Step 9

Lower oven temperature to 300℉.

Step 10

Plums: Wash and cut the plums in half. Working around the pit, slice around 8 slices per plum.

Step 11

In a stand mixer fitted with a whisk or in a large bowl with a handheld mixer, whip the egg whites until foamy and white (Note: it's imperative that the egg whites contain no yolk specks. If they do, this will affect the quality of the meringue). Gradually add in the granulated sugar and whip together until soft peaks form (2-3 minutes). Remove whisk and using a spatula, fold in the powdered sugar and mix gently until just combined.

Step 12

Sprinkle some bread crumbs or cornmeal onto the bottom of the baked tart crust to ensure the bottom is crisp after the plums are baked in it. Next, in a circular pattern arrange the plum slices. Spread the meringue mixture on top and make sure there are no 'holes' in between the plums. Using a box grater or your hand, break up the remaining uncooked tart dough and sprinkle on top.

Step 13

Bake in oven for 60-65 minutes. After 65 minutes, turn off oven and let it sit in the oven for an additional 10-15 minutes. Remove and let cool.