Simple Berry Galette

Bahan-bahan (1 porsi)

• 1 and 1/4 cups (156g) all-purpose flour (spooned & leveled), plus more as needed
• 1/4 cup (30g) fine cornmeal
• 3 Tablespoons (38g) granulated sugar
• 1/4 teaspoon salt
• 1/2 cup (8 Tbsp; 113g) cold unsalted butter, cubed*
• 1/4 cup (60ml) cold buttermilk, plus more as needed
• 4 cups (about 600g) fresh or frozen mixed berries* (do not thaw & see Note)
• 1/4 cup (50g) granulated sugar
• 1 Tablespoon (7g) cornstarch
• 1 Tablespoon (15ml) fresh lemon juice
• egg wash: 1 large egg beaten with 1 Tablespoon milk
• coarse sugar for sprinkling