Centerpiece desert, which is a cross between a trifle and a tiramisu.
Spray baking sheet with non-stick spray
Bring both sugars and half and half to boil in medium saucepan over med-high heat; whisking to dissolve sugar.
Reduce heat to med-low and simmer 5 minutes; whisking constantly Add butter, vanilla and salt. Attach candy thermometer to pan and simmer without stirring until temperature reaches 260 F. Remove from heat and immediately add pecans. Transfer to baking sheet and spread. cool completely and cut into 1/4 inch pieces.
Using electric mixer, mix all ingredients in a large bowl until firm peaks form. Set aside 1/2 cup for use in pumpkin filling
Whisk pumpkin, brown sugar, cream, cinnamon, nutmeg, allspice, and salt in a large bowl to blend. Whisk in reserved mascarpone cream.
Spread 1/3 cup mascarpone cream over bottom of trifle dish (8"x5" or 12 to 14 cup capacity) Place layer of ladyfingers on top (about 1/2 of a 3-oz package). Sprinkle 1 1/2 TBLSP rum over ladyfingers. Spread 1/2 cup pumpkin filling over ladyfingers; spreading to edge. Sprinkle 1/3 cup pralines over. Follow with 1 cup mascarpone, then another layer of ladyfingers, followed by 1 1/2 TBLSP rum, 1 cup pumpkin filling and 1/3 cup pralines.. Repeat again with 1 cup mascarpone, ladyfingers, rum, and 1 cup pumpkin filling and pralines. Spread remaining mascarpone cream on top. Cover and chill overnight. (May be made 2 days ahead)) Keep chilled
Sprinkle 1 cup praline decoratively over the top.