Sweat the aromatics. In a slow cooker on the saute setting, begin the process of sweating by combining the olive oil, yellow onions, garlic, salt, and pepper. Stir occasionally until you see the onions are translucent, about 5 minutes. Deglaze with the red wine vinegar.

Braise veggies. Select the low heat setting on your slow cooker then layer in the bay leaves, water, carrots, squash, and beets. Slowly cooking fresh vegetable in a braising liquid is a great way to build layers of flavor for sauce making.

Immersion blend and finish seasoning sauce. Your vegetables need to be tender and how long this takes depends on your slow cooker. Once you can easily pierce each vegetable, remove the 3 bay leaves then use an immersion blender to puree into a thick sauce. Stir in the Italian herbs and the lemon juice to taste. If the beet flavor is overpowering, you can add more salt. Ladle the sauce into mason jars and refrigerate for up to 5 days or cool and freeze in airtight bags for up to 3 months.