For the pumpkin seed brittle, toast the pumpkin seeds in a 400 degree F oven for 4-6 minutes or until fragrant and light golden brown, set aside.
Place nonstick parchment paper (or oil the surface) on a large rimmed baking sheet. Heat the sugar, water, corn syrup and salt in a medium saucepan over medium-low heat until the sugar dissolves. Increase heat to medium and allow sugar mixture to boil.
Using a candy thermometer, boil until 270 degrees F. Add the butter, pumpkin pie spice and vanilla. Continue to boil until the thermometer reads 300 degrees F.
Remove pan from heat and add the pumpkin seeds and baking soda. Be careful, the mixture will bubble up. Stir until bubbles calm down. Spread mixture out on prepared pan and cool. Break brittle into small pieces and store in an airtight container up to several weeks. Place a sheet of waxed paper between layers.
For the toast, spread the Mascarpone or cream cheese on the toast. Spread the Maple Pumpkin Butter over cheese and top with bits of pumpkin seed brittle.