If you only learn one dessert sauce, make it crème anglaise. You can alter the flavoring very easily and it goes well with virtually any dessert. It also makes what may be the very best vanilla ice cream ever! You'll need three bowls to make this; stainless steel bowls are probably best.
½ cup milk (4 ounces)
½ cup heavy cream (4 ounces)
½ vanilla bean
4 egg yolks (2 ounces)
¼ cup sugar (2 ounces)
Mix the milk and cream in a small saucepan. Split the vanilla bean and scrape the seeds into the pan, then add the pod. Bring just to a simmer, then remove from the heat and let steep for 15 minutes or so to infuse the dairy with vanilla flavor.
Partially fill the largest bowl with equal parts ice and water, and set the larger of the remaining bowls on the ice. Set a strainer in place over that bowl.
After the vanilla has infused the dairy to your satisfaction, remove the vanilla pod, then return the pan to gentle heat and stir frequently. In the third bowl, quickly whisk the yolks and sugar together. Once the dairy reaches a simmer, remove it from the heat and whisk about a tablespoon of it into the yolk and sugar mixture. Continue adding the dairy to the yolk and sugar mixture slowly to avoid curdling.
Once the dairy, yolks, and sugar are fully incorporated, return the custard to the pan and return the pan to the heat. Stir constantly for 1-4 minutes until the custard coats the back of a spoon. Pour through the strainer into the bowl over the ice. Stir until cool, cover, and refrigerate. If it sits overnight the vanilla flavor will be more pronounced. Serve cold, room temperature, or even warm, as your dessert requires.
For a little variety, add a pinch of cinnamon or a shot of your favorite liquor or liqueur to the dairy instead of or in addition to the vanilla. If you want to make a larger quantity, use weights rather than volume measures or it might get a bit eggy. Crème Anglaise will keep in the refrigerator for several days.