make: /bin/sh: Command not found - makefile

Question

My environment:
I have recently installed MinGW and GNUWin32 on my Windows 10 pc.
I can compile with g++ successfully without using a make file.
With a makefile, make finds g++ to do compiles.
Problem:
My Clean rule is failing with:
make: /bin/sh: Command not found
make: *** [clean] Error 127
I edited my makefile to have only the following:
RM = C:\WFF\GNUWin32\bin\rm.exe
clean :
whoami
where rm
${RM} *.o *.exe
When I execute make, this is the result:
whoami
tilt
where rm
c:\WFF\GNUWin32\bin\rm.exe
C:\WFF\GNUWin32\bin\rm.exe *.o *.exe
make: /bin/sh: Command not found
make: *** [clean] Error 127
Observations:
whoami works
where works and finds rm.exe
but, through the macro substitution for ${RM}, rm.exe is not found
I tried both of the following with weird results:
executed the make file this way: make SHELL=cmd.exe
added this to the makefile: SHELL = C:\Windows\System32\cmd.exe
For each, make seems to
call cmd.exe
execute the comand whoami
and stops
I enter exit, and make continues
call cmd.exe
execute where rm
and stops
I enter exit, and make continues
etc.
If I enter exit too many times, the window is closed, which doesn't surprise me.
Question: any idea what I can do to debug this or solve it?