Pulse the flour and salt together in a food processor until combined. Add the chilled, cubed butter and pulse until the mixture resembles coarse breadcrumbs with some pea-sized pieces of butter remaining—this creates those flaky layers we want. Transfer to a bowl and stir in the apple cider vinegar, then add ice water one tablespoon at a time, stirring gently with a fork until shaggy dough just begins to form. Turn the dough onto a work surface and knead it gently 4 times to bring it together, then shape into a flat disk. Wrap in plastic and refrigerate for at least 1 hour—I always make this dough ahead so it's cold and easy to work with when I'm ready to assemble.

While the dough chills, beat the room-temperature cream cheese until smooth and creamy. Add the vanilla bean paste, salt, ground nutmeg, and lime zest, beating until well combined. Add the large egg and continue beating, then sift in the powdered sugar and mix until the filling is light and smooth. Set aside at room temperature.

Combine the hulled and sliced strawberries with the blueberries in a bowl. Drizzle with lime juice and sprinkle with the granulated sugar and cornstarch, tossing gently to coat. Let sit for 5-10 minutes so the berries release their juices slightly—the cornstarch will help thicken these juices during baking so your galette doesn't become soggy.

Preheat your oven to 400°F and line a large baking sheet with parchment paper. On a lightly floured surface, roll the chilled dough from Step 1 into a 14-16 inch circle. Transfer to the prepared baking sheet. Spread half of the cheesecake filling from Step 2 over the dough, leaving a 2-inch border around the edges. Arrange the fruit filling from Step 3 on top of the cream cheese layer, then dollop the remaining cheesecake filling over and around the berries.

Fold the 2-inch dough border up and over the filling, creating a rustic frame that partially encloses the fruit and cheese. Don't worry about it being perfectly even—that's part of the charm! Beat the remaining egg and brush it onto the exposed dough edges, then sprinkle generously with demerara sugar. Bake for 40-45 minutes until the crust is deep golden brown and you can see the fruit filling bubbling slightly at the edges. I like to rotate the sheet halfway through baking to ensure even browning.

Remove the galette from the oven and let it cool on the baking sheet for at least 15-20 minutes before serving. This allows the filling to set slightly while the crust remains crispy. Serve warm or at room temperature with whipped cream or vanilla ice cream if desired.