Step 1
Grind tomato flakes, red pepper flakes, and ¼ tsp. salt in spice mill or with mortar and pestle to a fine powder. Transfer spiced tomato dust to an airtight container; set aside.
Step 2
Combine turnips, butter, sugar, and miso in a medium high-sided skillet. Pour in water to cover turnips halfway (about 1½ cups). Bring to a boil, stirring to dissolve miso. Reduce heat to medium-low; simmer, uncovered, until turnips are tender and liquid is reduced by half, 7–9 minutes. Remove from heat; set aside.
Step 3
Cook pasta in a large pot of boiling salted water, stirring occasionally, until very al dente. Drain pasta, reserving 2 cups pasta cooking liquid.
Step 4
Meanwhile, bring potlikker to a boil in another large pot. Add turnip greens; cook until tender, about 2 minutes. Stir in pasta; reduce heat and cook, thinning with reserved pasta cooking liquid as needed to keep the sauce slightly brothy, until pasta is al dente, about 2 minutes. Season with salt and pepper.
Step 5
To serve, ladle pasta and greens into shallow bowls; top with reserved turnips and their sauce. Sprinkle reserved spiced tomato dust over; top with microgreens (if using) and Pecorino Romano.
