Preheat oven to 425°F.
In a food processor place flour, baking powder, salt, and sugar. Pulse a few times to combine all the ingredients.
Add in the butter and continue to pulse until the mixture forms resembles a coarse meal.
Transfer to a large bowl. Add the feta cheese, candied walnuts, and parsley.
Slowly add in the heavy cream while mixing with a spatula or wooden spoon.
Transfer to a floured surface and knead the dough until in comes together. The dough will be moist, but able to be rolled.
Using a rolling pin, roll out dough into the shape of a rectangle that is about 12" x 6" by ¾".
Cut the rectangle in half lengthwise. You will now have 2 rectangles that are 12" x 3".
Cut each rectangle into 6 pieces. Cut each rectangle across in order to make two triangles.
Line a baking sheet with parchment paper and place rectangles on top. Place in the freezer for about 10 minutes.
Brush with cream and sprinkle with nigella seeds.
Bake for about 15 minutes, or until cake tester comes out clean.
Serve with jam.