I created this pie for my dad, who loves peppers and blackberries, but had never had them together. It's super sweet, with a real kick of jalapeno flavor. Even my sister, who's a wuss about spiciness, loved it!
Preheat oven to 425 degrees F (220 degrees C). Place a baking sheet on the bottom rack of the oven.
Combine blackberries, honey, jalapeno peppers, and lemon juice in a large bowl. Mix 1/2 cup brown sugar and cornstarch together in a bowl; stir into blackberry mixture until brown sugar mixture is dissolved.
Mix flour and 1/2 cup brown sugar together in a separate large bowl; cut butter into flour mixture using a pastry blender or food processor until mixture forms pea-sized balls. Add ice water and mix with your hands until dough is well combined, adding flour if the mixture is too sticky and small amounts of water if the mixture is too dry.
Divide dough in half and roll each half into a 9-inch circle on a well-floured surface. Press 1 circle into a 9-inch pie dish.
Remove jalapeno peppers from blackberry mixture and discard. Slowly pour blackberry mixture into pie crust, leaving about 1/4-inch space between top of filling and top edge of pie crust.
Mix oats and 1/2 cup brown sugar together in a bowl; sprinkle over blackberry filling. Cover pie with second pie crust. Cut off excess edges from top crust and fold bottom crust edges over top crust edges, pinching to form a seal. Cut 2 slits in the top of crust for ventilation.
Place pie on the middle rack of the oven, centered over the baking sheet on the bottom rack to catch drips. Bake pie until crust starts turning golden, about 25 minutes. Reduce temperature to 350 degrees F (175 degrees C) and bake until entire crust is golden brown, about 40 more minutes.
For a spicier pie, leave the jalapeno slices in the pie to bake. Optional: Brush 3 tablespoons milk across the top crust to create an even gold look. Sprinkle white sugar onto the milk to make the pie look glossy.