Cut the bacon into strips 5-6mm (¼") thick across the width of the rasher.
Cut the baby shallots in half lengthways, then peel them and trim the root end.
Finely slice the garlic cloves.
Remove the outer leaves from the lettuce, trim the base, then slice each lettuce in half lengthways.
Run the peas under cold water to defrost them.
Heat a 30cm or 12" frying pan or skillet (non-stick) over a medium-high heat, and when hot, add the bacon and cook for 2-3 minutes.
When the bacon is starting to crisp, turn the heat up to high and add the butter, garlic and stir.
Push the ingredients to the side and place the onions in the pan, cut side down and sear for 3-5 minutes.
Once the onions have caramelised on the cut side, push them to the side of the pan with the bacon and place the lettuce cut side down in the centre of the pan.
Cook the lettuce for 3 minutes again until it starts to take on some colour.
Flip over the lettuce and pour the chicken stock into the pan, and reduce the heat to low. Flip over the lettuce and stir everything together, and cook for 2 minutes.
Add the peas, cream and black pepper and cook for a final minute or two before serving.