In a medium bowl, whisk together the whole wheat flour, cinnamon, baking soda, and salt. This step evenly distributes the spice and leavening so you don't get a bitter bite of baking soda in one spot. Set this bowl aside while you prepare the wet mixture.
In a separate bowl, beat the softened butter and brown sugar together until the mixture turns light and fluffy. This usually takes about two to three minutes with a mixer. Creaming properly here helps create a tender, not tough, cracker texture later.
Mix in the honey, milk, and vanilla extract until everything is fully combined and smooth. The mixture might look slightly separated at first, but keep mixing and it will come together. This is where most of that classic graham flavor develops.
Slowly add the dry flour mixture into the wet ingredients, mixing on low speed until a soft dough forms. Avoid overmixing at this stage, since too much mixing can make the crackers dense. The dough should feel slightly sticky but manageable.
Wrap the dough in plastic wrap and refrigerate for at least one hour. Chilling firms up the butter again, which makes rolling much easier and prevents excessive spreading in the oven. You can even chill it overnight if you want to prep ahead.
On a lightly floured surface, roll the chilled dough out to about ⅛-inch thickness. Keep the thickness even throughout so the crackers bake at the same rate. If the dough feels too soft while rolling, pop it back in the fridge for ten minutes.
Using a pizza cutter or sharp knife, cut the dough into even rectangles or squares, similar to store-bought graham crackers. Use a fork to poke a few holes into each piece, which helps steam escape and keeps the crackers flat.
Transfer the crackers onto a parchment-lined baking sheet and bake at 350°F for about 15 to 18 minutes, until the edges turn a light golden brown. Rotate the tray halfway through for even baking. Let them cool completely on the tray before handling, since they firm up as they cool.