In a large food processor, mix together flour, sugar, and sea salt, then add butter cubes and pulse until it resembles peas.
Add the crust mixture to a large bowl and add the water, kneading until dough comes together and can form into a disc. Then wrap the dough disc in parchment paper and refrigerate for at least 30 minutes.
Meanwhile, add blueberries, sage, sugar, tapioca, lemon juice, and nutmeg to a large bowl and set aside.
In another large bowl, make the topping. Combine flour, rolled oats, sugar, brown sugar, sea salt, nutmeg, and butter cubes. Mix and knead together until mixture is crumbly.
Line a half sheet pan with If You Care Parchment Paper, then remove the pie crust disc from the refrigerator and press into the pan, making sure to cover the entire surface and the edges.
Pour blueberry and sage filling into the crust and top with topping. Place in the oven for 45 minutes.
Once topping and crust are light golden brown and pie is cooked, remove from the oven.
Allow to cool on rack. Serve warm or room temperature with your favorite ice cream or frozen treat!
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