In a saucepan, melt the butter. Stir in the flour and cook for 1 minute. Whisk in the maple syrup and cream. Bring to a boil over medium heat, stirring constantly. Let simmer for 2 minutes. Pour into a bowl and cover with plastic wrap. Allow to cool partially. Refrigerate until lukewarm, about 45 minutes.
With the rack in the middle position, preheat the oven to 180°C (350°F). Line a baking sheet with parchment paper.
In a food processor, pulse the dry ingredients until the nuts are coarsely chopped. Add the melted butter and pulse for a few seconds until the mixture resembles coarse sand. Spread the mixture on the baking sheet. Bake for 6 minutes. Stir and bake until golden brown, about 6 minutes. Allow to cool completely.
In a bowl, whip the cream with the sugar and vanilla with an electric mixer until soft peaks form.
Set aside 30 ml (1 tablespoon) crumble. Divide the remaining crumble among six 250-ml (1-cup) glasses or dessert cups. Spoon the maple topping over the crumble and garnish with a generous dollop of Chantilly cream, leaving a border of maple topping. Sprinkle with the reserved crumble.
Refrigerate. You can refrigerate this dessert for 2 to 3 days.