Place the puff pastry slices next to each other and defrost at room temperature for about 10 minutes. In the meantime, clean and wash spring onions and cut them into rings. Mix crème fraîche with egg and season with salt and pepper.
Cut 5 mm wide strips from each side of the puff pastry squares. Brush the edges of the squares with water and place the strips on the edge. Place on a baking tray lined with baking paper.
Prick with a fork and brush with whisked egg yolk. Pre-bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 8 minutes. Wash the thyme, dab dry and put aside a little to garnish.
Remove the rest from the stems. Mix the thyme with the spring onions. Spread the spring onions in the middle of the tartlets and sprinkle with crème fraîche. Put goat's cheese on top. Bake in the oven at the same temperature for about 10 minutes.
Serve with cranberries and garnish with remaining thyme.