Two fire engines from Preston rushed to the scene in Sedgwick Street shortly before 9am.
Firefighters equipped with two breathing apparatus doused the flames using one hose reel before utilising a positive pressure ventilation unit to clear the home of smoke.
No injuries were reported, but the fire service said they hoped "buttering bread prior to placing it in the toaster is not a common practice".
"Preston Fire Station attending another cooking related fire this morning," a spokesman said.
"The occupants left the property and were waiting outside despite smoke alarms not working which we have replaced.
"We hope buttering bread prior to placing in the toaster is not a common practice. Not recommended."
Fire crews were in attendance for around 30 minutes.
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