Creating a curvature ramp from one level to another - from 2D to 3D

I am not sure if I explain it correctly. But basically creating a curvature ramp that goes from one level to another.
I’ve created the curve in 2D. Split it in two. Moved one of them a level up. But now I can’t figure out how to make the transition between the two.

blendSrfKeepingCurvature.3dm (262.0 KB)