Season the guinea fowl legs with salt and pepper. Heat oil in a roaster over medium-high heat and fry the legs until golden brown, about 5-8 minutes. Remove and set aside.
In the same roaster, sauté the diced onion over medium heat for 2-3 minutes until softened. Deglaze with the white wine, scraping up the browned bits, and simmer for 1-2 minutes.
Add the diced tomatoes, brown sugar, poultry stock, juniper berries, lightly pressed unpeeled garlic clove, bay leaf, and fresh thyme to the roaster. Stir to combine.
Return the guinea fowl legs to the roaster, placing them on top of the sauce. Transfer to the preheated oven and braise for 35-40 minutes until cooked through.
Remove the guinea fowl legs from the roaster and keep them warm on a plate. Remove the juniper berries, bay leaf, and garlic clove from the sauce and discard them.
If the sauce is too thin, simmer it on the stovetop over medium heat for 5-10 minutes to reduce and concentrate the flavors. Season with salt and pepper to taste.
In a bowl, lightly whip the cream for 1-2 minutes until soft peaks form (should not be stiff).
Fold the whipped cream and gin into the tomato sauce.
Serve the guinea fowl legs topped with the tomato-cream-gin sauce, accompanied by fresh white bread.