New video about Using Multiple Sketches and Datum Planes in FreeCAD

Hello everyone,
Quite new on CAD here, trying to design some simple parts to get some practice.
One question I couldn´t find an answer to anywhere online: Can I make a pocket at an angle on a body? Just to be clearer, I want to insert a hollow slot at 45º into a cube. I am working on Freecad v0.19, btw.

Many thanks!
Ariel