A question about browning meat for spaghetti bolognese
Kenji at Serous Eats pondered exactly this question at length. (emphasis mine)

And now we get to the most crucial phase of the process: the long cook. If you take a quick look back at that passage from Cook's Illustrated, they do make one good point: browning meat toughens it far more than simply simmering it. But we also know that browning adds flavor, right?
In fact, some very well-respected ragù recipes call for browning the ground meats until very brown, like the version that Mario Batali makes on The Chew. In that version, he cooks the meat until what he calls &quot;beyond brown&quot;. I've made that recipe (or variations close to it) a number of times and have even eaten what can be presumed to be the same sauce at two of his restaurants. It's absolutely packed with flavor, but I simply can't get over the dried nubs of meat you end up with when you brown ground meat past the last inch of its life.
Surely there has to be a way to get great browned flavor without having to reduce the tender meat to dry rubble?
In point of fact, the whole reason I was extra excited for Bolognese season to start this year was because of this slow-cooked tomato sauce technique I developed a few months back.
The concept is simple: rather than simmering a pot of tomato sauce in a pot on the stovetop, just transfer the whole thing to the oven. Not only does the oven deliver more even heat and better reduction with less mess, but it also creates delicious caramelized bits of tomato on the top surface of the sauce and around the edges of the pot which you can stir back into the finished sauce for richer, deeper, more complex flavor.

He's got another secret for his amazing Bolognese: Fish Sauce. (no joke) Umami bomb 

Doesn't that look good? He gets down and dirty with all of the explanation of his technique in the article linked to in the beginning of this answer.
The recipe (it's a beaut) is here
EDIT HA! I made it (with half the liver), and it turned out great!