Mustard Peppercorn sauce

1 Tbsp sugar
2 Tbsp tarragon or white wine vinegar
1/4 c dijon mustard
1/2 tsp salt
2 egg yolks
2 Tbsp green peppercorns, rinsed and drained
1 Tbsp unsalted butter
1/2 c heavy cream

In top of double-boiler, combine sugar, vinegar, mustard, salt, egg yolks and peppercorns. Whisk over hot water until thickened, about 5 minutes. Remove from heat and stir in butter. Allow to cool. Whip cream and fold into mustard sauce. Cover and refrigerate until serving time. the sauce may be made up to one week in advance. Serve with steak.