Meanwhile, pour off the fat in one of the skillets used for browning the meat. Add 1 tablespoon of the butter. Add the shallots, garlic and carrot and cook over moderate heat, stirring occasionally, until softened and just beginning to brown, about 6 minutes. Add the tomato paste and juniper berries and cook, stirring, for 2 minutes. Add the wine and cook over moderate heat, scraping up any browned bits stuck to the bottom of the skillet, until the sauce is slightly thickened and reduced to 1/2 cup, about 10 minutes. Add the demiglace and bring to a boil. Strain the sauce through a fine sieve into a small saucepan, pressing hard on the solids. Season the jus with salt and pepper and stir in the remaining 1 tablespoon of butter.