Select one of the base planes (XY/ZX/YZ) and click on the context menu command Insert new plan.... [Insert new plane...]

Under Type, select Layer with rotation [Plane with rotation] in the list box.

Example: Base plane XY rotated on X axis and shifted in direction of Z axis

Enter a number of degrees under Angle.

Select the Custom axis [Custom Axis] option in the list box under Rotate around [Turn around].

The rotation axis is defined via a direction vector, which you specify in the Rotation axis dialog area AND an axis point, which you specify under Point on axis.