Preheat the oven to 325ºF and line a baking sheet with parchment paper.

In a medium bowl, whisk together the almond flour, coconut, and sweetener. Stir in the melted butter until the mixture begins to clump together.

Transfer to the mixture to the prepared baking sheet and spread out into a thin layer. Top with another piece of parchment and press down to help it stick together.

Remove the top piece of parchment and bake 18 to 25 minutes, until the crumble is golden brown. Remove from the oven and let cool completely to crisp up, then break into small pieces with your fingers.

Combine the blueberries, the sweeteners, and the water in a medium saucepan over medium heat. Bring to a boil, then lower the heat to a simmer and cook until the berries are soft enough to be mashed, about 7 minutes.

Remove from heat and stir in the lemon zest. Sprinkle the glucomannan overtop and whisk to combine. Let cool completely.

Prepare the condensed milk: In a medium saucepan over medium heat, combine 1 cup of the cream, the almond milk, ¼ cup of the Swerve, the allulose, and the vanilla extract. Bring to a simmer, then reduce the heat and simmer 20 minutes.

Remove from heat and add the butter. Let melt, then stir in the vanilla extract. Sprinkle the surface with the glucomannan and whisk to combine. Let cool to room temperature.

In a large bowl, beat the remaining 1 ½ cups cream with the remaining powdered sweetener until it holds stiff peaks. Gently fold in the cooled cream/almond milk mixture until no streaks remain.

Spread half of the vanilla ice cream in a freezer-safe container and dollop half of the blueberry sauce overtop. Sprinkle with half of the crumble and swirl with a knife to combine.

Repeat with the remaining ice cream, the sauce, and the crumble. Swirl until well mixed but still streaky.

Cover tightly and freeze until firm. Depending on what sweetener you use, this can take 8 to 24 hours.