Preheat oven to 350˚ and lightly grease an 8x8 pan.
Combine pastry flour, cornmeal, baking powder, and sea salt in a bowl, stir to combine. In a separate bowl, whisk together eggs, maple syrup, walnut oil, and milk. Pour into dry ingredients and stir until batter is combined. Pour into prepared pan and bake until golden and springs back when pressed, 25-30 minutes. Let cool slightly.
Once cornbread has cooled, carefully cut cornbread into 1/2" cubes and place 2 cups of the cubed cornbread into a bowl. Add 1 tablespoon olive oil and rosemary, tossing until cornbread is covered. Place on a baking tray and return to oven. Bake for 13-15 minutes until cornbread is firm and toasted, stirring halfway through.
To roast vegetables, peel and cut sweet potatoes into 1/2" cubes. Toss with quartered Brussels Sprouts, onion, 1 tablespoon oil, salt, and pepper. Place in the oven and roast until vegetables are tender and browning, 40-50 minutes.
While everything bakes, combine olive oil, balsamic vinegar, mustard, and maple syrup in a jar with a lid. Shake well until dressing is combined.
To serve, combine roasted vegetables, toasted cornbread, spinach, and blue cheese in a large bowl. Drizzle dressing on top and toss until everything is well coated.
Notes
*Cornbread had be made the day ahead. However, I've also been known to bake the cornbread, let cool slightly, and then re-toast all while the vegetables are roasting.