One recipe galette (or pie) dough. Refrigerate for at least one hour, up to a day. Roll out onto floured surface into a flat disc.
For filling, mix 4-5 cups berries (whatever you fancy) with 1/3 cup sweetener (honey, maple syrup, agave, etc.) a pinch of salt, a pinch of spice (nutmeg, cinnamon, etc.) juice of half a lemon and 4ish T flour.
Transfer dough into cast iron skillet (or onto a baking sheet lined with parchment paper) and spoon filling into center of dough, leaving a 2 inch border. Fold edges over, brush with egg white (or heavy cream) and sprinkle with Demerara sugar. Bake at 400' (until the dough turns a nice golden color, ~15 min.) then finish baking for another 30-50 minutes at 350' until the juice bubbles out of the sides. Let cool one hour.
Serve with ice cream, or whipped cream. My go to whipped cream recipe is simple: whisk 1 cup heavy cream, 2 T granulated sugar, and 1 tsp vanilla bean paste (or vanilla extract) until it stiffens.