Blueberry Ginger Slab Biscuits

These pillowy biscuits are layered with blueberry jam and chewy candied ginger, but feel free to use any other combination of preserves and nuts or dried fruit. Consider plum preserves laced with five spice powder, marmalade paired with pistachios and pecans, or a mix of cherries and chopped dark chocolate.

nonstick vegetable oil spray or unsalted butter, for pan
2 Tbsp. baking powder
2½ tsp. Diamond Crystal or 1½ tsp. Morton kosher salt
½ tsp. ground ginger
4½ cups all-purpose flour, unbleached (563 g)
½ cup + 2 Tbsp. old-fashioned oats (45 g)
¼ cup + 4 tsp. sugar (50 g)
½ cup (1 stick) unsalted butter, chilled
1 Tbsp. lemon zest, finely grated
1 large egg
1 cup sour cream (not low fat)
¾ cup buttermilk
1 tsp. pure vanilla extract
½ cup blueberry or blackberry jam
2 tsp. lemon juice, freshly squeezed
½ cup fresh or frozen blueberries, preferably wild
¼ cup candied ginger, chopped

Preheat oven to 425°F (220°C/200°C fan, Gas Mark 7). 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.

Makes 12 servings.