Preheat oven to 425 degrees F. Have ready a parchment lined baking sheet.
In a mixing bowl or the bowl of a food processor, thoroughly stir together the flour, sugar, baking powder and salt.
Cut up the butter and work it into the dry ingredients. If using a food processor, just pulse until mixture is coarse.
In another mixing bowl, whisk together the cream, egg and vanilla.
Add the flour mixture to the cream mixture and stir with a heavy duty scraper or big spoon just until moistened, then turn onto a floured mat and press down flat. Fold in thirds, sprinkling with flour as needed and pressing down again to work in any excess flour and press in any butter bits. You should see a lot of little hard butter bits.
If adding blueberries of chocolate chips, press frozen blueberries into the dough, then fold the dough over onto itself so that the blueberries (or any other add-in) are within the dough.
Push the dough together to form a circle that's somewhere between ½ and 1 inch thick. The thickness will affect bake time. Cut the circle into 8 wedges and arrange the wedges a few inches apart on the baking sheet. Brush tops with a little additional cream (or you can use additional egg) and sprinkle with coarse sugar if desired. Bake for 13 to 18 minutes or until lightly brown around the edges.