36 ounces frozen blackberries, thawed
1/2 cup sugar
2 tablespoons cornstarch
1 1/2 teaspoons grated lemon zest
1 tablespoon lemon juice
1 cup baking mix
1/4 cup sugar + 2 teaspoons sugar
2 ounces unsalted butter, melted (1/2 stick)
1/3 cup buttermilk
1/2 teaspoon vanilla extract
1/8 teaspoon fresh ground nutmeg
Preheat oven to 375 degrees F.
Combine sugar, cornstarch, and salt in a large bowl. Add blackberries and toss gently to coat; add lemon zest, lemon juice and syrup and mix to combine. Transfer to 9-inch deep dish pie plate, place pie plate on parchment-lined sheet pan, and bake 30 minutes or until filling is hot and bubbling around edges.
To prepare biscuit topping, whisk baking mix and 1/4 cup sugar in a large bowl to combine.
In small bowl, whisk melted butter, buttermilk and vanilla until well combined.
In second small bowl, mix 2 teaspoons sugar with ground nutmeg; set aside.
Remove filling from oven and increase oven temperature to 425 degrees F.
Add reserved wet ingredients to dry ingredients; stir gently until just combined. Divide dough into 8 equal pieces and drop pieces evenly over hot berry filling, leaving at least 1/2 inch space between.
Sprinkle dough with reserved sugarnutmeg mixture and bake until filling is bubbling and biscuits are golden brown and cooked through, about 20 minutes.