Preheat oven to 350°F (175°C).

In a mixing bowl, combine flour, rolled oats, 1/2 cup brown sugar, and 1/2 cup butter or margarine.

Mix until the mixture resembles coarse crumbs using an electric mixer on low speed.

Press the crumb mixture evenly into an ungreased 13 x 9-inch pan.

Bake the crust for 20 minutes at 350°F (175°C).

While the crust is baking, prepare the filling. In a separate mixing bowl, combine pumpkin, evaporated milk, eggs, sugar, salt, cinnamon, ginger, and cloves.

Beat the filling ingredients well until thoroughly combined.

Pour the pumpkin filling evenly over the pre-baked crust.

Bake for an additional 20 minutes at 350°F (175°C).

In a small bowl, combine chopped walnuts or pecans, 1/2 cup brown sugar, and 2 tablespoons butter or margarine.

Sprinkle the nut mixture evenly over the pumpkin filling.

Return the pan to the oven and bake for an additional 15 to 20 minutes, or until the filling is set.

Remove from the oven and let the pumpkin pie squares cool completely in the pan on a wire rack.

Once cooled, cut into 2-inch squares.

Serve and top with a dollop of cream if desired.