Small dice the carrots and onion. Small dice means to cut into ¼ inch pieces. This is critical as the small size pieces are perfect for sauteing. The larger your pieces, are the worse your saute will be. This causes less flavor to develop, as there is lower surface area in contact with the heat source. 

Saute vegetables in olive oil and salt until browned (about 10 minutes).

Add in the ground beef and garlic. Cook until browned (about 10 minutes). Depending on the size pan you are using, you might be running low on space here. If you risk layering meat on top of the vegetables, remove the vegetables from the pan and just cook the meat on its own.

Add in the wine, milk, tomatoes, and tomato paste. Do not add the milk in first since there is a small risk it could burn, giving your bolognese a burnt flavor. Pour the milk in after you have added the wine.

Simmer uncovered for 3 hours. If sauce becomes dry, add ½ cup milk to maintain consistency.