Wash the kale heart and cut it into 1 cm strips. Rinse the bacon and cut into 1 cm lardons. Peel and slice the onions.
Season the pigeons with salt and pepper. In a casserole dish, melt the butter and brown the pigeons on all sides for 15 minutes. Finish by sprinkling with gin, flambé, and remove the pigeons. Keep warm.
Add the bacon to the casserole and brown for 2 minutes over high heat. Add the onions and cook for 5 minutes over low heat, stirring frequently. Stir in the kale, season with salt and pepper, cover, and cook for 10 minutes. Add the juniper berries, mix well, and set aside.
Meanwhile, debone the pigeons and cut into large pieces.
Preheat the oven to 210°C (gas mark 7).
Roll out the shortcrust pastry to 1/2 cm thickness, forming a 35 cm circle. Line a 25 cm tart pan, allowing the pastry to overhang.
Spread one-third of the kale mixture on the base, top with half the pigeon meat and slices of semi-cooked foie gras, then finish with the remaining kale. Fold the overhanging pastry towards the center, pleating as you go. Brush with egg yolk and bake for 35 minutes.
Serve the golden-brown pie garnished with tarragon leaves.
