Freeze butter until firm, 10 to 20 minutes.

In a large bowl, whisk together flour, peanut butter powder, sugar, baking powder, and salt. Using a pastry blender or 2 forks, cut in frozen butter until pieces are pea-size.

In a small bowl, whisk together cold cream and cold sour cream. Using a fork, gradually stir cream mixture into flour mixture until dry ingredients are moistened. (It’s OK if dough is crumbly or shaggy in parts.)

Turn out dough onto a clean surface; gently knead or fold 8 to 11 times just to bring dough together. Shape into a rough 5-inch square. Wrap in plastic wrap, and freeze for 10 minutes.

On a lightly floured surface, roll or pat dough into a rough 12×5-inch rectangle, lightly flouring rolling pin as needed; fold into thirds like a letter. (Dough may start out crumbly but will come together with each fold.) Rotate dough 90 degrees; repeat rolling and folding process. Wrap in plastic wrap, and freeze for 15 minutes.

On a lightly floured surface, roll dough into a 12×5-inch rectangle, lightly flouring rolling pin as needed; fold into thirds like a letter. Roll into an 8×4-inch rectangle; divide into 2 (4-inch) squares. (For best accuracy, divide dough by weight.) Wrap in plastic wrap, and freeze for 15 minutes.

Working with one half at a time, preshape dough into a rough circle; roll or pat into a 8- to 8½-inch round (about a scant ¼ inch thick). Wrap in plastic wrap, and freeze dough circle. Repeat with remaining dough.

Line a baking sheet with parchment paper.

Dollop and spread Thick Strawberry Jam evenly over 1 dough circle, leaving a ¾- to 1-inch border around edges. Brush border with egg. Top with remaining dough round; pinch together edges, and tuck underneath disk. Pinch closed any seams in bottom and sides of disk; shape into a 7½-inch round (about ¾ inch thick). Using a serrated knife, cut dough into 6 wedges, wiping blade between cuts. Place at least 2 inches apart on prepared pan. Freeze until firm, 30 to 40 minutes.

Preheat oven to 350°F (180°C).

Place a second baking sheet underneath pan with scones. (See Note.) Brush tops of scones with egg.

Bake until golden brown, a wooden pick inserted in center comes out clean, and an instant-read thermometer inserted in center registers 200°F (93°C) to 205°F (96°C), 22 to 30 minutes, loosely covering with foil during final 5 minutes of baking to prevent excess browning. Carefully remove from pan, and let cool on a wire rack for 25 minutes. Serve warm, or let cool completely. Drizzle with Peanut Butter Glaze before serving.