Prep Fennel: Cut a very thin sliver off the dirty bottom. Then trim stalks and fronts from the bulb. Thinly slice the lighter part of the stalk and set aside separately from the fronds. Cut each bulb through the center. Then cut each half into wedges with a portion of the core in each wedge to hold it together. You will get 8-10 wedges per bulb, depending on how large they are.
Heat large skillet over medium-high heat. Swirl in the olive oil and add fennel wedges in a single layer. You may have to do this in two batches. Sprinkle with salt and pepper. Use tongs to flip after first side is brown, about 2 minutes per side. Transfer to a dish as they're finished. Continue until all fennel wedges have been seared.
Add the garlic and sliced fennel stalks and cook, stirring constantly until garlic is fragrant, about 1 minute. Deglaze the pan with the white wine. Whisk miso into the broth and then add to the pan. Bring to a simmer, while stirring.
Return the fennel to the pan, on top of the liquid. There should be enough room for all the fennel in one layer now. Top with thyme sprigs. Turn the heat down to simmer on low, cover and let steam for 20 minutes. Fennel should be super tender when pierced with a fork, sweet and caramelized.
Remove fennel wedges to a plate. Leave pan on stove and let sauce thicken for a minute. Spoon a bit sauce over the fennel, and pour the rest into a small dish. Garnish with the fronds and/or some fresh thyme leaves.