Combine the sugar, water, vanilla bean, and lemon juice in a medium (3-quart, let’s say) saucepan. Bring to a boil, then turn down the heat and leave to simmer gently. Meanwhile, peel the pears, cut them in half from stem to blossom, and remove the cores with a sharp knife and a teaspoon. Slip them into the simmering syrup, and let them cook gently until they are tender to the point of a knife. You’ll see that as they cook, they begin to look somewhat translucent, more yellow than white. That’s what you want. They should take anywhere from 15 to 30 minutes to cook, and if some are ready before others, just lift them out and transfer them to a plate. When all the pears are tender, take the pan off the heat, put back any pears that you’ve taken out, and leave them to cool in the syrup.

When you’re ready to eat, put the chocolate into a small, heavy-bottomed saucepan with the coffee and the cream. Warm slowly over low heat, stirring occasionally, until the chocolate has melted. Once the chocolate has softened, stir until it is very smooth. Then stir in the butter. Remove the pan from the heat.

Drain the pears, and put them in bowls or a serving dish. Serve with the warm sauce alongside, so that each diner can pour on as much as he or she wants.

Note: Any sauce left over can be warmed gently in a microwave – be sure to give it a stir every 10 seconds, and don’t let it get too hot – or over a double boiler.