Whisk together spelt flour, brown sugar, baking soda, salt, and cinnamon in a large bowl. Add cold, cubed butter and rub it into the flour using your fingertips or a pastry cutter until the mixture resembles coarse meal with pea-sized bits.

Stir the honey (or molasses), vanilla, and 2 tablespoons of cold milk together. Pour into the flour mixture and mix gently with a fork until a dough starts to coalesce. If it feels too dry to hold together, add the remaining tablespoon of milk. Shape into a flat disc, wrap in plastic, and chill in the fridge for at least 30 minutes.

Preheat oven to 175°C (350°F) and line two baking sheets with parchment paper. Roll out the chilled dough directly onto parchment paper to about 3mm (1/8-inch) thick. Trim edges into a clean rectangle, then cut into individual squares or rectangles using a pizza cutter or fluted pastry wheel. Dock (prick) each cracker multiple times with a fork to prevent puffing.

Transfer the parchment with the cut crackers onto baking sheets. Bake for 12–15 minutes until the edges are golden brown and firm. Turn off the oven, prop the door open slightly, and let the crackers sit inside for 5 minutes to fully dry out for maximum snap. Cool completely on a wire rack.