Baked cheddar and scallion soup

700g/1 1/2lb onions, sliced
4 tbsp Irish butter
350ml/12fol dry white wine
45g/3tbsp cream flour
3 1/2 pints oxo stock
salt and pepper
1 egg yolk
3 1/2floz single cream
300g Irish cheddar
1 bunch spring onions, thinly sliced
8-12 slices stale baguette, toasted

Pre-heat oven to 200C/400F/Gas 6. Sweat the onions in half the butter without letting them color. Add the wine and continue to cook until the wine almost evaporated. Meanwhile, make a light roux by melting the remaining butter in a small pan. Add the flour and cook gently without coloring for 2 minutes, stirring. Allow the roux to cool slightly then whisk the stock onto the roux until you have a smooth, lightly thickened stock. Add this to the onions with the bouquet garnish and a little