KSP v1.5: Single stage, nonstop trip to Eve and back: World first stock, unrefueled SSTK from Eve.

Stock parts and physics, one very long spaceplane. References: Astrobond: First Eve SSTO proof of concept: Stratzenblitz75; First fully reusable Eve mission: Kergarin Aerospace; First fully functional Eve SSTO: My own asteroid-shenanigans Eve single stage mission: