Step 1Heat the milk in a small saucepan until bubbles just form around the edges. Pour it into a medium bowl and cool to lukewarm.
Step 2Add the yeast, sugar and 1 1/2 cups flour. Mix well. Cover tightly with plastic wrap and set aside in a warm spot for 45 minutes, until light and spongy.
Step 3Bring a small saucepan of water to a boil. Add pancetta cubes; reduce heat and simmer for 10 minutes. Remove the pancetta and drain on paper towels.
Step 4Place the pancetta in a skillet and cook over medium-low heat until cooked but not crisp, about 8 to 10 minutes. Drain on paper towels and set aside.
Step 5In the bowl of an electric mixer fitted with the paddle attachment, cream the butter at medium speed. Beat in the salt. Beat in the eggs one at a time.
Step 6Reduce the speed and gradually add 2 cups flour. Add the yeast mixture and beat until smooth, adding more flour as needed to make a sticky dough that clings together in a ball.
Step 7Change the paddle attachment to the dough hook and knead 15 minutes, until very satiny. Add the lardons and pepper and knead until evenly dispersed (you may have to finish with your hands).
Step 8Scrape the dough into a buttered bowl, turning to grease all sides. Cover tightly and set aside in warm spot until doubled in bulk, about 1 hour.
Step 9Punch the dough down, form into a ball again, cover again and let rise another hour.
Step 10Heat the oven to 375 degrees. Butter two 9-by-5-inch loaf pans or two souffle dishes. Punch the dough down once more. Divide it in half and press each half into a prepared loaf pan or souffle dish. Cover and let rise 30 minutes.
Step 11Brush the tops of the loaves with beaten egg yolk. Bake the bread until deep golden brown and hollow-sounding when tapped on the bottom, 23 to 25 minutes (try not to overbake; the brioche will dry out). Cool on a rack before slicing. (Waiting a day will make the bread even easier to slice.)