Add the vegetable broth, broccoli florets, and minced garlic to the slow cooker. Cover and cook on low for about 40 minutes, until the broccoli is very tender and the house is filled with a rich garlic aroma.
Use an immersion blender directly in the slow cooker to blend the mixture until smooth and velvety. Be careful of hot splashes and ensure no chunks remain.
Stir in the miso paste, incorporating it until fully dissolved into the soup, adding a deep, savory umami flavor.
If using, pour in the heavy cream to enrich the soup’s texture and create a smooth, creamy consistency. Stir well to combine.
Taste the soup and season with salt and pepper as needed, adjusting the flavor to your liking.
Once heated through and well seasoned, ladle the soup into bowls, and optionally garnish with a drizzle of cream or a sprinkle of finely chopped herbs for color and extra flavor.