To prepare cake, combine milk, 1/3 cup sugar, and yeast in the bowl of a stand mixer; let stand 10 minutes. Stir in 1/4 cup butter, 1 teaspoon vanilla, and egg.
Weigh or lightly spoon spelt flour and 6 ounces Kamut flour into dry measuring cups; level with a knife. Combine flours, gluten, and salt. Add to milk mixture; beat on low speed with dough hook just until combined. Beat on medium-low speed 5 minutes (dough will be quite wet and sticky, but do not add additional flour). Scrape dough into a large bowl coated with cooking spray; coat top of dough with cooking spray. Cover and let rise in a warm place (85°F), free from drafts, 1 hour or until almost doubled in size.
Turn dough out into an 11 x 7–inch glass or ceramic baking dish coated with cooking spray (do not punch dough down). Pat dough evenly into bottom of dish; top with nectarines. Cover and let rise 1 hour or until doubled in size.
Preheat oven to 350°F.
To prepare streusel, weigh or lightly spoon 1.625 ounces Kamut flour into a dry measuring cup; level with a knife. Combine flour, 1/3 cup sugar, cinnamon, 1/4 teaspoon salt, and ginger in a small bowl. Drizzle with 1 tablespoon butter, oil, and 1/8 teaspoon vanilla; toss well to combine. Uncover dough; sprinkle evenly with streusel. Bake at 350°F for 30 to 35 minutes or until golden brown and a wooden pick inserted in center comes out clean.
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