In a large mixing bowl, combine 1 ½ cups of all-purpose flour and ¼ teaspoon of salt. Cut in ½ cup of cold, unsalted butter until the mixture resembles coarse crumbs. Gradually add 4–5 tablespoons of ice-cold water, stirring until the dough comes together. Wrap it tightly in plastic wrap and refrigerate for at least 30 minutes.

Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

In a mixing bowl, combine 2 cups of mixed berries, ½ cup of sugar, 2 tablespoons of cornstarch, and 1 tablespoon of lemon juice. Let it sit for about 10 minutes.

Once chilled, transfer the dough to a floured surface. Roll it out into a circle about ¼ inch thick. Use a heart-shaped cutter to cut out heart shapes and place them onto the prepared baking sheet.

Spoon the berry filling into the center of each heart-shaped dough piece, leaving a 1-inch border around the edges. Fold the edges of the dough over the filling, crimping the corners to create a decorative edge.

In a small bowl, whisk together 1 egg with a tablespoon of water to create an egg wash. Brush the edges of each galette with the egg wash.

Bake the galettes for 25–30 minutes, or until the crust is golden brown and the filling is bubbly.

Let them cool for about 10 minutes, then dust the tops lightly with powdered sugar before serving.