Preheat the oven to 400°F (200°C).
- Wrap each beet in foil and roast on a baking sheet for 45–60 minutes, or until fork-tender.
- Let the beets cool, then peel and slice into ¼- to ½-inch rounds.
- Optional: Use a round cutter to trim beet slices for uniform stacks.
- In a small bowl, mix goat cheese with 1 tbsp olive oil and a pinch of black pepper until spreadable.
- Assemble stacks by alternating beet slices and goat cheese layers, gently pressing to form stacks.
- In a separate bowl, whisk together Dijon mustard, vinegar, olive oil, thyme, and optional honey. Stir in toasted walnuts. Season with salt and pepper.
- Drizzle vinaigrette over the beet stacks just before serving.
- Garnish with extra thyme or chopped walnuts, if desired.