Pour your whipping cream into your mixer with whisk attachment. Whip on high for about 1 minute, add your sugar and vanilla and continue to mix until a semi-firm peaks form.
Place pecans on a baking sheet and toast in a 350 degree F. oven for 10-15 minutes until aromatic. Let cool.
Place in your mason jar your brownie circle, your whipped cream, chocolate syrup and pecans, repeat one more time until you've reached the top.
If you are going to serve them later, leave room at the top to be able to put the lid on until ready to serve.
When ready to serve, top with whipped cream, chocolate syrup and pecans.