You can make the soufflé mixture a couple of hours ahead of time and finish with the eggwhites just before assembling and baking.
60 gmbutter, coarsely chopped, plus extra, melted, for brushing and to serve2leeks, thinly sliced1garlic clove, finely chopped2 tspthyme, plus extra, to serve20 gmfresh fine white breadcrumbs60 gmfinely grated parmesan65 gmplain flour380 mlmilk80 gmGruyère, coarsely grated4eggs, separated½ cup eachfinely chopped chives and flat-leaf parsley, plus extra to serveWholemeal crêpes160 ml(1/3 cup) milk100 gm(1/3 cup) wholemeal flour30 gmmelted butter, plus extra, for brushing2eggs
For wholemeal crêpes, process ingredients and 1 tsp salt in a food processor to combine, then set aside for 1 hour to rest. Heat a 21cm-diameter crêpe pan over medium-high heat, brush lightly with butter, add 80ml crêpe batter and swirl pan quickly to coat evenly. Cook until bubbles appear on the surface (1 minute), turn and cook until base is golden (30 seconds), then set aside on a plate. Repeat with remaining batter until you have 5 crêpes. Store interleaved with baking paper and wrapped in plastic wrap until required. Crêpes will keep refrigerated for 3 days.
Melt 20gm butter in a saucepan over medium-high heat, add leek and garlic, sauté until tender (4-5 minutes), add thyme, stir then set aside.
Preheat oven to 200C. Line the base of a buttered 20cm springform cake tin with a round of buttered baking paper, butter-side up. Cut a piece of baking paper long enough to line the sides of the cake tin with a 5cm collar extending above the sides. Butter the collar and line sides of cake tin, with the butter side facing out. Combine breadcrumbs and 20gm parmesan in a bowl, season to taste and tip into cake tin. Shake tin to coat base and sides evenly with parmesan mixture and tip out any excess.
Heat remaining butter in a saucepan over medium-high heat until foaming, add flour and stir until smooth and combined. Gradually add milk, whisking continuously until thick, smooth and glossy (6-8 minutes). Season to taste and remove from heat. Add Gruyère and remaining parmesan, beat to combine, then add egg yolks one at a time, beating well between each addition. Add herbs and leeks, then set aside.
Whisk eggwhites and a pinch of salt in an electric mixer until firm peaks form. Fold a third of the eggwhite into the cheese mixture, then repeat with remaining eggwhite.
Place a crêpe in the base of the prepared cake tin, spread a quarter of the soufflé mixture over, top with another crêpe and repeat until all crêpes and soufflé mix are used, finishing with a crêpe. Brush a little melted butter over top crêpe and bake until golden and puffed (30-35 minutes). Serve immediately, drizzled with a little extra butter and scattered with extra herbs.