Combine all-purpose flour and spelt flour in a bowl. Add salt, pepper, cayenne, garlic powder, and onion powder. Whisk until combined. Add olive oil and water. Stir mixture together with your fingers until a dough starts to come together; knead into a smooth ball.

Wrap dough in plastic wrap and let rest about 1 hour in the fridge or at room temperature.

Preheat the oven to 375 degrees F (190 degrees C).

Divide dough in half. Press and roll 1 half into a rectangle about 1/8-inch thick, sprinkling with flour as needed to prevent sticking. Transfer dough onto a silicone-lined baking sheet.

Lightly brush entire rectangle with a small amount of water. Sprinkle sesame seeds and poppy seeds all over; top with fleur de sel. Press topping gently into the dough before flipping over. Use a pizza cutter to slice dough lengthwise into strips, then diagonally into diamonds. Repeat rolling, topping, and cutting the remaining dough.

Bake in the preheated oven until golden brown and crispy, about 20 minutes.

Flip crackers over in their pans and let cool completely.