My Welsh rarebit starts in a saucepan, not on the toast

Some evenings nobody wants a proper dinner, but everybody is hungry. It is dark, the heating has only just come on, and the fridge holds a wedge of Cheddar, half a pint of milk and a loaf that is a day past its best. On those evenings I make Welsh rarebit. For years I thought of it as fancy cheese on toast, and I made it that way: slices of cheese laid on bread and pushed under the grill. It was fine, but the cheese went oily and slid off. The habit that changed it is simple. My rarebit starts in a small saucepan, and the toast comes second.

I make the sauce in a small saucepan on a low hob. A knob of butter goes in, about 25 g, and when it foams I stir in 25 g of plain flour and let it cook for a minute without colouring. Then I add 100 ml of milk, or half milk and half ale if there is an open bottle, a little at a time, stirring until I have a very thick, smooth paste. It should look almost too thick, like a spread rather than a pouring sauce. That is what holds the cheese on the bread later.

Off the heat goes 200 g of grated mature Cheddar, a teaspoon of hot mustard, a few good shakes of Worcestershire sauce and plenty of black pepper. I stir until the cheese has melted into the paste and it turns glossy and stretchy. If it seems stiff, a spoonful more milk loosens it. I taste it from a clean spoon, and it should be sharp, savoury and a little hot from the mustard. This is the whole secret of a good rarebit: the cheese is not just cheese any more, it is bound into something that can sit on toast without splitting.

Meanwhile the bread is toasted on both sides, four thick slices, ideally from a firm white or brown loaf, not the softest sliced bread. I toast them properly, because the topping goes on wet and a pale slice will go soggy underneath. Then I spread the cheese sauce thickly right to the edges, so the crusts do not burn bare, and put the slices on a tray under a hot grill.

Now I stand and watch. In two or three minutes the top puffs, bubbles and turns a deep golden brown, with darker freckles where the mustard and Worcestershire sauce catch. The edges of the toast go crisp. When it is spotted and bubbling all over, it comes out. I cut each slice in half on the diagonal and we eat it straight away, standing at the worktop if necessary, with a few slices of tomato or a bit of pickle on the side.

What I love about this way is that the topping stays where you put it. There is no puddle of fat on the plate and no bare toast in the middle. The rarebit is soft and rich under the crust, the bread is crunchy underneath, and the kitchen smells of toasted cheese and mustard. It is also a very kind way to use bread that is too dry for sandwiches.

If I make a double batch of sauce, the rest goes into a covered tub, and I cool it and put it in the fridge within two hours, as the Food Standards Agency advises for leftovers, and use it within two days. The next evening it only needs spreading on fresh toast and grilling until it bubbles and is piping hot. Contains milk, wheat (gluten), mustard and, in most Worcestershire sauces, fish, so I check the label; ale also contains gluten.

So my rarebit is a little pan of sauce, thick toast and five patient minutes at the grill. What do you put on toast on the nights when nobody wants a proper dinner?