Preheat oven to 375°.
Obtain or prepare pastry rolled out to ⅛” thickness. Cut into 4” rounds and line 12 medium-sized tart pans or muffin cups. Do not prick.
Pour boiling water over raisins. Let soak until edges of raisins begin to turn white. Drain.
Cream butter and brown sugar together thoroughly.
Add salt, corn syrup (or maple syrup), beaten egg, vanilla, and lemon juice. Combine only until blended.
Fold in the drained raisins.
Spoon mixture into the unbaked tart shells, filling each about ⅔ full.
Bake in preheated 375° oven for 20 to 25 minutes. (Option: bake at 400° for 5 minutes and reduce to 375° for 20 minutes).
Do not allow the filling to boil or it will turn hard.