Maple Oatmeal Berry Scones with Maple Bourbon Drizzle

Name: Maple Oatmeal Berry Scones with Maple Bourbon Drizzle
Ingredients: 2 cups (9 ounces) all-purpose unbleached flour (I use King Arthur all-purpose unbleached); 1/2 cup (2.25 ounces) old-fashioned rolled oats (reserving 3 tablespoons to mix in at step 4) plus extra for the tops of the scones; 1 tablespoon baking powder (I use Red Star brand); 1/2 teaspoon kosher salt; 6 tablespoons cold unsalted butter; 3/4 cup frozen mixed berries (I use blueberries, raspberries, blackberries); 3/4 cup cold heavy cream, plus extra for brushing on the scones; 1/4 cup maple syrup, plus extra for brushing on the scones and for the icing (or substitute runny honey); 1 cold large egg; 1 teaspoon vanilla; maple sugar, or granulated sugar, for sprinkling on the scones