Preheat oven to 400 degrees. Toss sweet potatoes with oil, salt, & cayenne & spread on a baking sheet (line with parchment or tinfoil for easy clean up) & roast for 40- 45 minutes, until soft & caramelizing on the edges (use convection if you’ve got it, but it won’t take as long). Meanwhile, heat butter in a heavy-bottomed soup pot & sauté onions until translucent. Add garlic & thyme & sauté until golden. Add roasted sweet potatoes & stock & bring to a boil. Lower heat & simmer for about 10 minutes. Remove from heat & puree soup with an immersion blender or food processor in batches until smooth. Return to low heat, add half & half, stirring frequently, until it returns to a gentle simmer – do not allow it to boil. Add freshly grated pepper & nutmeg to taste, cover & keep warm while you make croutons. Heat oil in a skillet & add cubed bread. Stir until starting to brown. Turn off heat & sprinkle with blue cheese. Cover for a minute to melt cheese. Ladle soup into bowls & carefully place some hot cheesy croutons on top.