-
1
Preheat oven to 400 degrees Fahrenheit. Line a baking sheet with parchment paper.
-
2
In a large bowl, mix together the flour, sugar, baking powder, baking soda, and salt.
-
3
Add the dry ingredients and the frozen butter to a food processor and pulse until it forms a coarse meal. Transfer back to the large bowl (in lieu of a food processor, you can also grate the butter into the dry ingredients and work it in with your fingers).
-
4
In a small bowl, whisk together the sour cream, egg, and water, and then add it to the flour and butter and mix together until just combined. Gently fold in the blackberries and the walnuts.
-
5
Transfer the dough to a lightly floured surface and shape it into a 7-inch circle. Cut the dough into 8 slices and transfer it to the lined baking sheet. Bake for 20-25 minutes, or until the scones are golden brown and firm when lightly pressed in the middle. Let cool for about 10 minutes.
-
6
In a food processor, cream together the butter and sugar (you can also use an electric mixer). Slowly add the eggs, egg yolks, vanilla bean seeds, and lemon juice, and pulse until combined.
-
7
In a medium-sized pan, heat the mixture over low heat, stirring occasionally, until it begins to look smooth, about 10 minutes. Increase the heat a bit, just below simmering, and heat for an additional 10 minutes, stirring occasionally, until the mixture has thickened significantly and easily coats a spoon. Do not boil the curd, you don't want to scramble the eggs!
-
8
Once the curd has thickened, remove it from the heat and give it a good stir. Transfer it to a lidded container and refrigerate. The curd will continue to thicken as it cools.
