What a great question! I wasn't asked to do that, but I don't even know where to start.
I know of several designs that used but a single device and friend N2CQR took on that challenge, but I think ended up using two devices.
Here is a LINK to a whole lot of CW transceiver projects and one that caught my eye if only from the very clever aspect -- the Toaster CW transceiver. The designer took a defunct toaster case and built a rig inside the former breakfast special enclosure.
Now in my book he would have gotten extra points if he kept the toaster function AND built the rig inside the case. There is nothing like a warm bagel and bagging some DX.
We started with a minimum part count premise and some of those projects in the listing are anything but simple. I think the operative word is simple as that connotes minimum part count, less opportunities to screw up, a short time from parts collection to on the air. That short time frame solves the instant gratification prevailing feeling among 99% of today's hams... I want it and I want it now!
Simple also connotes topologies involving no filters, no frills and knowing stuff. N2CQR and KK4DAS clearly demonstrated with their direct conversion receiver project that simple is not simplistic. Over 100 units based directly on their design have been built around the world. They even garnered a prestigious award from the ARRL for their effort. So that would be a place to start.
Later on, the DCR could be upgraded with a Crystal Filter and other frills to provide narrow bandwidth single signal reception. BTW the DCR works well copying SSB signals and coupled with a DSB transmitter now adds a phone capability.
Simple transmitters like the Tuna Tin Two or the Michigan Mighty Mite would be good candidates for the RF generation end of stick.
Rex Harper's, W1REX, TTT Kit
For our demographic described in a recent blog
post you can buy a kit from W1REX so no excuses that you would have to start from scratch!
Now the real problem is how to switch from transmit to receive. It could be something as simple as a DPDT switch.
The starting point is just that as a vast number of hams are still pondering which end of the soldering iron is hot. CW radios using the DCR and simple transmitters like the TTT, offer a chance to homebrew a radio that has roots in the 1930's. It is also a steppingstone in that converting over to a Double Sideband Transmitter now moves you off the CW only playing field.
N6QW's 20M CW Transceiver
Them that know can make things go.
73's
Pete N6QW