Mix together the flour, thyme, baking soda and salt. Add the water, oil and honey, knead into a soft dough, cover and leave to rest at room temperature for approx. 30 mins. On a lightly floured surface, roll out the dough into a rectangle approx. 2 mm thick. Cut into rectangles (6 x 10 cm), place on a baking tray lined with baking paper, brush with water. Sprinkle with the mixed seeds and fleur de sel.
Approx. 12 mins. in the lower half of an oven preheated to 200°C. Remove from the oven, leave to cool on a rack.
Using the whisk on a hand mixer, beat the butter and lemon juice for approx. 2 mins. until light and fluffy, season with salt. Serve the butter and radish with the crispbread.