From the Cooks Illustrated Article: Best Bolognese Sauce (Jan 1999)

Italian Pasta Beef Marinades, Rubs, Sauces, and Condiments 

Beef Bolognese Sauce

Don't drain the pasta of its  cooking  water  too  meticulously  when
using  this  sauce;  a little water left clinging to the noodles will
help distribute the very thick sauce evenly into the noodles, as will
adding  an  extra  2 tablespoons of butter along with the sauce.  Top
each serving with a little grated  Parmesan  and  pass  extra  grated
cheese at the table.  If doubling this recipe, increase the simmering
times for the milk and the wine to 30 minutes each, and the simmering
time once the tomatoes are added to 4 hours.

Makes 3 cups, enough to sauce 1 pound pasta
 
3 tablespoons unsalted butter 
2 tablespoons minced onion 
2 tablespoons minced carrot 
2 tablespoons minced celery 
3/4  pound    ground beef or lamb/pork/beef "meatloaf" mix
              Table salt 
1 cup         whole milk 
1  cup        dry white or red wine 
2 cans (28 ounces each) whole tomatoes , packed in juice, chopped
              fine, with juice reserved

This rich, smooth, thick sauce  is  best  over  fresh  pasta;  it  is
especially good with fettuccine or cheese ravioli.


1.  Heat butter in large, heavy-bottomed Dutch oven over medium heat;
add  onion,  carrot,  and  celery  and  saute  until softened but not
browned, about 6 minutes.  Add ground meat  and  1/2  teaspoon  salt;
following  illustration below, crumble meat with edge of wooden spoon
to break apart into tiny pieces.  Cook, continuing to  crumble  meat,
just  until  it  loses its raw color but has not yet browned, about 3
minutes.

2.  Add milk and bring to  simmer;  continue  to  simmer  until  milk
evaporates and only clear fat remains, 10 to 15 minutes. Add wine and
bring to simmer; continue to simmer until wine evaporates, 10  to  15
minutes  longer.   Add  tomatoes and their juice and bring to simmer;
reduce heat to low so that sauce continues  to  simmer  just  barely,
with  an  occasional  bubble  or two at the surface, until liquid has
evaporated, about 3 hours (if lowest burner setting is  too  high  to
allow  such  a  low  simmer,  use  a  flame tamer or a foil ring (see
related Quick Tip) to elevate pan). Adjust seasonings with extra salt
to taste and serve. (Can be refrigerated in an airtight container for
several days or frozen for several months.  Warm over low heat before
serving.)

White wine works best with the lamb/pork/beef mixture, while red wine
is best if you just use beef. Also, a beef/pancetta (ham) mixture was
found to work quite well with red wine.