Preheat oven to 325°F. Prepare Easy Layers! 6 in. Cake Pan Set with vegetable pan spray.
In large bowl, stir together flour, cinnamon, baking powder, ginger, coriander, nutmeg, baking soda and salt.
In large bowl, beat butter and brown sugar with electric mixer until light and fluffy. Add eggs one at a time, mixing well after each. Add flour mixture alternately with buttermilk, beating until just combined. Divide evenly into pans.
Bake 19-22 minutes, or until toothpick inserted in center of cakes comes out clean. Cool in pan on cooling grid 5 minutes. Remove from pans; cool completely on grid.
While cakes bake, make filling. Prepare a cookie pan with parchment paper. In medium skillet, stir together pecans, granulated sugar, cinnamon, coriander, and nutmeg. Cook over medium-high heat, stirring constantly until sugar turns a dark amber color, about 4-5 minutes. Immediately spread nuts onto prepared cookie pan in a single layer. Cool completely. Chop roughly. Reserve 1/4 cup.
In large bowl, gently stir mascarpone, confectioners' sugar, cream, and vanilla extract until just combined. Reserve 1/4 cup. Fold in remaining 3/4 cup chopped pecans.
To assemble, cut the crowns off of each cake layer. Place first layer on serving plate. Spread 1/4 of icing with candied pecans to edge; top with second layer. Continue with remaining cake layers and icing, leaving sides of cake bare. Ice top layer with reserved 1/4 cup plain icing and sprinkle with reserved 1/4 cup candied pecans.