Mix together flours, sugar, and sea salt. Slowly add in butter, olive oil, and water, mixing well, until dough forms. Dough should be slightly sticky.
Divide dough in two, and roll out each ½ on a slightly floured surface. Lightly wet the dough and sprinkle with sea salt and fennel (or other toppings of your choosing).
Cut the crackers into squares (I used my middle three fingers as a width guide).
Transfer the crackers onto lightly floured baking sheets and bake for 10-12 minutes, watching carefully at the 10 minute mark so they do not burn.
Transfer to a cooling rack for 10 minutes before serving. You can store these in an air-tight container for a week or so, if they get a little stale, put them back in the oven at 350 for a couple of minutes.
Recipe by Things I Made Today at https://www.thingsimadetoday.com/2013/03/18/sea-salt-and-fennel-crackers/