slowly but surely
At a slow or incremental pace but making steady, dependable progress. I've been writing my thesis slowly but surely—it will probably take me all year to finish it, but it's getting there! A: "Hey, how's the new novel coming along?" B: "Ah, slowly but surely!"
slowly but ˈsurely
used for describing definite but slow progress in something: Attitudes to women at work are changing slowly but surely.