In a large mixing bowl, combine the mayonnaise and sour cream together, stirring until fully blended and smooth. Add the grated onion paste, sugar, mustard, vinegar, salt, pepper, and paprika. Whisk everything together until the dressing is completely homogeneous and the sugar has dissolved. I like to taste the dressing at this point and adjust the vinegar or salt to your preference—it's much easier to balance flavors before adding the coleslaw.

Add the coleslaw mix to the creamy dressing from Step 1 and gently fold it together until every strand of cabbage and carrot is evenly coated. Don't overmix or you'll bruise the vegetables. Transfer to a serving bowl or storage container, cover, and let the slaw sit in the refrigerator for 30 to 60 minutes before serving. This resting time allows the cabbage to soften slightly and the flavors to meld together beautifully—I find the slaw tastes noticeably better after it's had time to sit.