Generously salt and pepper the roast on all sides.
Cut onion in half, then cut off both ends and peel off the skin.
Cut 3 to 4 carrots into 2-inch slices - or use the pre-cut ones and skip this step.
Heat a large saucepan over medium high heat.
Add 1 to 2 tbsp olive oil to pan.
Once oil is very hot, add onion halves and brown on all sides.
Remove the onion to a plate on the side.
Add in carrots, again sautéing until they have a slight hint of brown color.
Remove carrots to the side.
If needed, add 1 more tbsp. oil to pan.
Place roast in pan, browning on all sides.
Remove the roast to the slow cooker, but do not turn it on yet.
With the stove burner still on medium high, pour in 1 cup of beef broth and deglaze the pan (scrape off the brown bits left by onion and carrots).
Once pan is deglazed, carefully pour the contents into your slow cooker on top of the roast.
Pour in the remaining 1 or 2 cups of beef broth. You want it to cover the meat halfway.
Add the onions and carrots to the slow cooker.
Add the rosemary and thyme, making sure to submerge the sprigs in the beef broth.
Cook on low heat for 7 to 8 hours.