Notes: Pastry chef Les Carmona of the Lodge at Sonoma, in Sonoma, California, uses yellow hot dog mustard in this tart. Bake the pastry before making filling. If making tart up to 1 day ahead, cool, cover, and chill. Bring to room temperature or heat in a 350° oven for about 20 minutes before serving.
1/2 cup (1/4 lb.) butter or margarine
2/3 cup sugar
2 1/2 tablespoons all-purpose flour
1 1/2 teaspoons dry mustard
2 tablespoons prepared mustard (see notes)
1 large egg
4 cups coarsely chopped peeled Golden Delicious apples (about 1 3/4 lb.)
In a 1- to 1 1/2-quart pan over medium heat, melt butter and stir often until golden brown, 5 to 7 minutes. Remove from heat.
Meanwhile, in a bowl, with a mixer on medium speed, beat sugar, flour, and dry mustard until well blended. Beat in prepared mustard and egg. Add hot butter in a thin, steady stream, beating until mixture is cool, 2 to 3 minutes. Gently stir in apples.
Spoon apple mixture into warm baked butter pastry and spread level. Sprinkle cheese streusel evenly over filling. Set tart on a foil-lined 12- by 15-inch baking sheet.
Bake in a 350° regular or convection oven until streusel is golden brown, 45 to 55 minutes. If tart edges brown excessively, drape lightly with foil. Cool on a rack about 1 1/2 hours. Remove pan rim. Cut tart into wedges.