Begin this recipe a day before baking. In the bowl of stand mixer fitted with dough hook, add flour, sugar, yeast and salt and mix, about 1 minute.
In a separate bowl, whisk together 1/3 cup warm milk and 3 eggs. Slowly add milk mixture to dry ingredients, mixing at medium speed until sticky dough forms, 5 to 8 minutes. Scrape down sides of bowl if necessary to ensure ingredients are well-incorporated. Add butter, one tablespoon at a time, waiting until each is fully incorporated to add the next. Once all butter has been added, continue beating 10 minutes on medium-high speed, until dough is soft, sticky and elastic in texture, and comes away instead of sticking to side of bowl. Add mini chocolate chips and mix to incorporate.
Place dough in a lightly oiled bowl, at least 3 times the size of dough, cover and allow to rise in a warm place for 90 minutes, until doubled in size. Do not touch the dough. Cover the bowl. Place in refrigerator overnight (8 to 10 hours). Dough will continue to rise a bit more.
Remove dough from fridge and punch down to release air. Gently knead dough into a smooth ball. Generously butter your Brioche Baker. Remove a small piece of dough, about the size of a golf ball, and set it aside. Roll remaining dough into a smooth ball and place into prepared brioche pan. Use thumbs to create an indent in the center. Roll smaller piece of dough into a smooth ball. Insert ball into indent of dough already in Brioche Pan. Place uncovered Brioche Pan in a warm place for 1-3 hours, until the dough has at least doubled in size. Because dough is cold it will take longer than normal to rise, time will depend on temperature of the room.
Preheat oven to 400°F. Place a metal baking sheet in the oven. In small bowl, whisk 1 egg and 1 teaspoon milk. Gently brush top of brioche with egg wash. Place Brioche Baker on metal baking sheet in oven. Bake for 30-35 minutes, or until lightly golden. If browning too quickly, after 15 minutes, lightly cover with foil to stop over-browning. Brioche is cooked if the internal reading is 185°F on a digital thermometer. Remove brioche from oven and allow to cool in pan for 5-10 minutes before carefully unmolding. Let brioche cool completely on a wire rack before serving. Serve with soft butter and raspberry jam.