Preparation Preheat oven to 425°F. Lightly coat a 13x9" baking pan or dish with nonstick spray. Whisk baking powder, salt, ground ginger, 4½ cups (563 g) all-purpose flour, ½ cup (45 g) oats, and ¼ cup (50 g) sugar in a large bowl to combine. Grate butter into dry ingredients on the large holes of a box grater, then lightly toss to coat. Add lemon zest and toss again. Freeze 10 minutes. Whisk egg, sour cream, buttermilk, and vanilla in a medium bowl to combine. Add all but 1 Tbsp. egg mixture to flour mixture and mix with a fork just until combined. Set remaining egg mixture aside for brushing over biscuits. Knead mixture in bowl with your hands until it roughly comes together. Turn out dough onto a lightly floured surface and gently pat together. Dusting with flour as needed, gently roll out to a 16x12" rectangle. Stir jam and lemon juice together in a small bowl. Spread over half of dough, staying just shy of edges. Scatter berries and candied ginger over. Fold side of dough without toppings up and over filling and gently press to seal. Using a bench scraper or a knife, cut biscuits into 12 portions. Arrange portions as they were cut in prepared pan. Brush with reserved egg mixture and sprinkle top with remaining 2 Tbsp. oats and 4 tsp. sugar. Bake biscuits until puffed and golden, 30–35 minutes. Transfer pan to a wire rack and let cool 10 minutes before serving.