In a medium bowl, whisk together the whole wheat flour, all-purpose flour, brown sugar, cinnamon, baking soda, and salt.
Add the cold, cubed butter and use a pastry cutter or your fingertips to work it into the flour mixture until it looks like coarse crumbs.
Stir in the oil, honey, molasses, vanilla, and 3 tablespoons of milk. Mix until a dough forms. If it seems dry, add the remaining milk 1 teaspoon at a time until the dough holds together.
Form the dough into a disk, wrap it in plastic wrap, and refrigerate for 30 minutes.
When ready, preheat oven to 325°F. Line two baking sheets with parchment paper.
On a lightly floured surface, roll the dough very thin, about ⅛ inch thick.
Cut into squares or rectangles, about 2 ½ × 2 ½ inches. A pizza cutter works well. Transfer them to the prepared baking sheets.
Prick each cracker several times with a fork or skewer to prevent bubbles during baking.
Lightly sprinkle the crackers with a cinnamon-sugar mixture (if using).
Bake 10 to 14 minutes, until lightly golden and dry to the touch. Rotate the pans halfway through for even baking.
Let crackers cool completely on a wire rack. They will crisp further as they cool.
Keep crackers in an airtight container at room temperature for up to 1 week, or crush into homemade graham cracker crumbs for pie crusts or desserts.