How to Make It
Preheat oven to 425°F. Prick potatoes all over with a fork. Place potatoes on a microwave-safe plate; cover with damp paper towels. Microwave at HIGH 10 to 12 minutes or until tender. Let cool slightly, about 10 minutes. While potatoes cool, place cauliflower and 1/2 cup of the water in a large microwave-safe bowl. Cover with plastic wrap and Microwave at HIGH 8 to 10 minutes or until tender; drain.
Transfer cauliflower to a food processor along with remaining 1/2 cup water. Process until mixture forms a coarse and thick puree, about 15 seconds.
Peel potatoes and pass through ricer into a large bowl. Stir in cauliflower puree until thoroughly blended. In batches, add flour until just combined and a soft dough forms. The dough will be moist.
On a lightly floured surface, divide dough into 8 equal pieces; cover with a clean kitchen towel until ready to use. Roll each piece of dough into a 3/4-inch-thick rope. Cut ropes into 1-inch pieces, and transfer to 2 large rimmed baking sheets coated with cooking spray. Brush tops of gnocchi lightly with oil. Bake in preheated oven until browned on the bottom and cooked through, 10 to 12 minutes. Transfer to 4 serving bowls.
Meanwhile, melt butter in a medium skillet over medium. Cook, stirring often, until butter turns golden brown, 2 to 3 minutes. Carefully add stock and return to a simmer over medium. Simmer until sauce is slightly reduced, about 5 minutes. Remove from heat and stir in salt, pepper, capers, lemon juice, and parsley. Pour about 3 tablespoons sauce over pasta in each bowl, and toss to combine. Sprinkle with Parmesan. Serve immediately.