Step 1

Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.

Step 2

Trim the stalks off the fennel, setting the green fronds to the side to later use for garnish, if desired. Trim the root ends to create a flat surface; there is no need to remove the core. Slice fennel into 1/4- to 1/3-inch slices and place on the baking sheet.

Step 3

Whisk together olive oil, vinegar, garlic, thyme, salt, and pepper in a small bowl. Brush over the fennel slices.

Step 4

Roast in the preheated oven until fennel is soft and caramelized, 25 to 30 minutes, turning slices over halfway through. Remove to a serving platter and garnish with green fronds, if desired.