Preheat your oven to 200°C (or 180°C for fan ovens) or Gas Mark 6.
Hold the peppers over an open gas flame until they turn black all around.
Place them in a bowl, cover with cling film, and let them sit for 1 to 2 minutes.
Take the peppers out of the bowl and peel off the charred skin.
Rinse the peppers under running water to remove any remaining skin.
Remove the seeds and set the peeled peppers aside.
Arrange on a baking tray the red peppers skin-side up, shallot halves (cut side down), plum tomatoes, and garlic cloves
Drizzle them with olive oil.
Bake on the top rack of the oven for about 15-30 minutes or until the shallots are cooked.
Melt the butter in a large pan over medium heat.
Add the roasted shallots, peeled peppers, and garlic.
Pour in the hot stock and cook for 5 minutes.
Puree the mixture using an immersion blender, until smooth.
Return it to the pan to warm