For the Crust & Topping:
Preheat oven to 350°F. Grease a 9x13 baking pan.
Stir together oats, flour, baking powder and salt. Set aside.
Using electric mixer on medium speed, beat butter and brown sugar until light and fluffy. Add eggs, one at a time, mixing well after each addition. Mix in vanilla.
Reduce mixer speed to low. Gradually add oat mixture, mixing just until combined.
Set aside about 1 cup of crust mixture for the topping.
Transfer remaining mixture to prepared pan. Spread evenly in bottom of pan and about 1/4 inch up sides.
Bake for 12 minutes. Set aside.
For the Filling:
Place brown sugar and butter in heavy, medium-sized saucepan. Cook over medium heat, stirring occasionally until butter is melted and mixture is combined. Bring to low boil, stirring occasionally, and cook until thickened, about 3-4 minutes.
Remove pan from heat. Carefully add cream (mixture will bubble) and stir to combine. Stir in vanilla.
Spread butterscotch evenly on top of partially baked crust.
Drop remaining crust mixture in small portions on top of butterscotch layer. Sprinkle with pecans.
Bake 25 to 30 minutes, or until golden brown. Cool completely before cutting into bars.