Peel the beetroot, cut in half lengthwise and then cut crosswise into slices approx. 1 cm thick. Cut the slices of cheese crosswise into thirds. Layer both in a greased, ovenproof dish (approx. 2 l) so that the cheese slices slightly overlap the beetroot.
Mix together the milk and eggs. Finely chop the tarragon, add along with the salt, mix well. Pour the sauce over the beetroot and cheese. Cut the bread into cubes and sprinkle over the top.
Bake for approx. 20 mins. in the lower half of an oven preheated to 220°C.