Preheat oven to 350°F and line a rimmed baking sheet with parchment paper.
Toss 1 pound blackberries, 2 tablespoons sugar, and 1 tablespoon bourbon together in a medium bowl and refrigerate until ready to eat, at least 30 minutes but up to 24 hours.
Finely chop 1/2 cup pecans and use a fork to stir them into a large bowl with 1 1/4 cups flour, 1/2 cup sugar, 3/4 teaspoon salt, and 1/4 teaspoon cinnamon or cardamom.
Stir 1/2 cup of cubed butter into the nut mixture until pea-sized clumps form. It’s ok if there are still parts that are very sandy and loose. Get in there with your fingers, it’s easier.
Spread crumble over the parchment-lined baking sheet and bake, stirring halfway through, until light golden, 20 to 25 minutes. Remove immediately if it starts to brown around the edges, we are NOT looking for browning here! Transfer the parchment paper to a cool countertop or cooling rack to let it cool.
Scoop the fruit into bowls. Scoop ice cream over top and sprinkle crumble over everything.
Keep leftover crumble in the freezer for up to 3 months.