In a medium sized saucepan, fry the bacon over moderately high heat, stirring occasionally, for 6 to 8 minutes or until it is crisp and has rendered most of its fat.
With a slotted spoon, remove the bacon from the pan and set it aside to drain on kitchen paper towels.
Reduce the heat to moderate and add the butter to the pan.
When the foam subsides, add the onions and fry them, stirring occasionally, for 8 to 10 minutes or until they are golden brown.
Remove the pan from the heat.
With a slotted spoon, remove the onions from the pan and add them to the bacon.
Using a wooden spoon, stir in the flour, salt and pepper into the pan to make a smooth paste.
Gradually add the stock, stirring constantly and being careful to avoid lumps.
Add the bouquet garni and the reserved onions and bacon.
Return the pan to the heat.
Bring the liquid to the boil, stirring constantly.
Stir in the peas and reduce the heat to low.
Cover the pan and simmer for 6 to 8 minutes, stirring occasionally, or until the peas are tender.
Remove the pan from the heat and remove and discard the bouquet garni.
Spoon the mixture into a warmed serving dish.