Step 1

Preheat the oven to 325°F. Line a baking sheet with parchment paper. In a stand mixer fitted with the paddle attachment, or in a medium bowl using your hands, combine the flour, granulated sugar, butter, sprinkles, brown sugar, vanilla, baking soda, and salt. Mix on medium speed until the butter is mostly incorporated and the batter creates pea-sized pebbles.

Step 2

Use your hands to break up the batter into a gravel onto the baking sheet tray. Bake until the crumble is evenly crisped and a light golden brown, rotating the pan halfway through baking, 12 to 15 minutes. Let the crumble cool completely on the baking sheet.

Step 3

Break up any large chunks so the crumble is a uniform pea-sized gravel. Place crumble on the baking sheet in the freezer until frozen, about 30 minutes. If not using within a few hours, transfer to a freezer-friendly container and freeze for up to 2 months.

Step 4

Combine the sugar, dry milk, and xanthan gum in a small bowl and stir well. Pour the tapioca syrup into a medium pot and stir in the whole milk. Add the sugar mixture and immediately whisk vigorously until smooth. Set the pot over medium heat and cook, stirring often and adjusting the heat if necessary to prevent a simmer, until the sugar has fully dissolved, about 3 minutes. Remove from the heat.

Step 5

Add the cream and whisk until fully combined. Transfer to an airtight container and refrigerate until well chilled, at least 6 hours, or for even better texture and flavor, 24 hours. It can be further stored in the fridge for up to 1 week or the freezer for up to 3 months.

Step 6

Measure out 3 cups of the ice cream base. Stir in the salt and vanilla extract(s) into the ice cream base. Pour the ice cream base into an ice cream maker and turn on the machine. Churn just until the mixture has the texture of soft serve, 30 to 40 minutes, depending on the machine.

Step 7

In one quart or two 1-pint freezer-friendly containers, alternate spoon 8 layers of the ice cream and birthday cake crumble in the quart container or 4 layers in the pint containers, drizzling about 1 tablespoon blackberry jam in a spiral over each layer. The goal is to get the perfect ratio of ice cream, crumbles, and jam in each scoop.

Step 8

Cover with parchment paper, pressing it to the surface of the ice cream so it adheres, then cover with a lid. It's okay if the parchment hangs over the rim. Store it in the coldest part of your freezer (farthest from the door) until firm, 6 to 8 hours. The ice cream will keep in the freezer for up to 6 months.