300 gmcoarsely grated Gruyère, plus extra to serve200 gmcrème fraîche2 tspDijon mustard2 tbspcoarsely chopped flat-leaf parsley and chervil, plus extra to serve12 slicesleg ham off the bone, coarsely torn500 gmcherry tomatoes, on the vine1½ tbspolive oil1 tspred wine vinegar1 tspthymeFor brushing and drizzling:melted butterBuckwheat crêpes500 ml (2 cups)milk110 gm (¾ cup)plain flour100 gmbuckwheat flour100 gmbutter, melted and cooled3eggs
For buckwheat crêpes, process ingredients and 1 tsp sea salt in a food processor until smooth and combined, transfer to a jug, cover and refrigerate overnight to rest. Brush a 25cm-diameter crêpe pan with a little melted butter. Stir crêpe mixture, pour 2-3 tbsp into pan, swirling quickly to thinly coat base, and cook, turning once, until browned on each side (30 seconds-1 minute each side). Transfer to a plate lined with baking paper and repeat with remaining butter and batter, wiping out pan with absorbent paper between crêpes (stir batter occasionally and thin with a little extra milk to a pourable consistency when required, as batter will thicken while standing). Store crêpes between layers of baking paper covered with plastic wrap until required.
Combine Gruyère, crème fraîche, mustard and herbs in a bowl and season to taste. Working with one crêpe at a time, place crêpe on a work surface, spread with Gruyère mixture, scatter with ham, then fold into quarters and place in a baking dish brushed with melted butter. Repeat with remaining crêpes, overlapping crêpes in dish. Cover with plastic wrap and refrigerate until required.
Preheat oven to 200C. Spread tomatoes on an oven tray, drizzle with oil and vinegar, scatter with thyme and season to taste. Roast until skins split (10-15 minutes) and keep warm.
Drizzle crêpes with melted butter, scatter with remaining Gruyère, cover with foil and bake until bubbling and warmed through (8-10 minutes). Serve warm, scattered with roast tomatoes and extra herbs.