Preheat oven to 350°F. Prepare Mini Whoopie Pie Pan with vegetable pan spray.
In large bowl, sift together flour, cocoa, baking powder, baking soda and salt.
In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg and vanilla extract; beat until well combined. Alternately add flour mixture and buttermilk in three additions, beating until just combined. Spoon one tablespoon batter into each cavity.
Bake 9-11 minutes or until tops of cakes spring back when touched. Cool in pan 3 minutes. Cool completely on cooling grid.
For icing: beat shortening and butter in large bowl with electric mixer until light and fluffy. Add cocoa, milk and vanilla; beat well. Gradually add sugar, one cup at a time, on medium speed; scrape bowl often. Continue to beat on high speed until light and fluffy.
To assemble: Place one cake in bottom of treat pop. Top with 1 tablespoon caramel and 1 tablespoon pecan pieces. Pipe a swirl of buttercream from back edge following the curve of the container, then filling in the center. Continue layering until treat pop is full. Top with additional pecans and caramel, if desired.