Buttermilk Biscuits With Curry Gravy

Name: Buttermilk Biscuits With Curry Gravy
Ingredients: 2 Tbsp. (heaping) sugar; 2¾ tsp. baking soda; 1½ tsp. baking powder; 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt; 5 cups (625 g) all-purpose flour, plus more for surface; 1½ cups (3 sticks) plus 2 Tbsp. chilled unsalted butter, cut into pieces; 2 cups buttermilk; 1 medium onion, coarsely chopped; 2 medium carrots, peeled, coarsely chopped; 5 garlic cloves, chopped; 2 tsp. vegetable oil; 8 oz. ground beef; 8 oz. ground pork; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; Freshly ground black pepper; 5 Tbsp. unsalted butter; 3 Tbsp. all-purpose flour; ½ tsp. curry powder (such as S&B); ½ tsp. ground turmeric; 4½ tsp. low-sodium soy sauce; 2 tsp. fish sauce; 3 cups low-sodium chicken broth; 2 oz. hot Japanese curry sauce mix (preferably House Foods Vermont Curry or S&B Golden Curry); ¼ cup heavy cream; Thinly sliced scallions and kimchi (for serving; optional)