Burning the Arduino Bootloader

Using an Arduino Uno as the ISP

TL;DR:

Select the correct port in Tools > Port
Load the ArduinoISP sketch from Files > Examples into the Arduino that will function as the programmer.
Select “Arduino as ISP” under Tools > Programmer
Select the correct target microcontrller type in Tools > Board (e.g. Arduino/Genuino Uno for ATMEGA328P-PU)
Wire up the target microcontrller to the Arduino that's functioning as the programmer.
Select Tools > Burn Bootloader

I currently get the following warning:

avrdude: WARNING: invalid value for unused bits in fuse “efuse”, should be set to 1 according to datasheet This behaviour is deprecated and will result in an error in future version You probably want to use 0xfd instead of 0x05 (double check with your datasheet first).

Things seem to work right now, but it looks like there might be trouble ahead.