Set the oven to 350°F (180°C) on the fan setting. Gently heat the milk (⅔ cup/150 ml) in a small pot, stopping before it boils. Add the honey (7 tbsp/100 ml), butter (2½ tbsp/35 g), and cinnamon (1 tbsp), and stir until everything melts together. Reserve a little butter for the tin.
Beat the eggs (3 large) in a second, larger bowl until evenly mixed. Keep whisking as you add the warm honey milk with cinnamon in a slow stream.
Tip in the buckwheat flour (14 tbsp/100 g) along with the baking powder (1 tsp). Whisk to a runny batter without any lumps.
Peel the washed apples (8 medium). Use seven for the batter and save one for decorating.
Cut the apples into thin pieces. A knife gives sturdier slices than a mandoline. Coat them at once in the juice of the lemon to prevent browning.
Add the slices to the batter and turn them carefully with a rubber spatula (or use your hands) so each one is covered. Hold back the slices of one apple for the top.
Place parchment paper on the base of a 9-inch (24 cm) springform tin and rub the butter around the sides. Transfer the apple batter and level it with the spatula, pressing the fruit down a little.
Spread the reserved slices across the top.
Set the baking pan in the center of the oven and bake for 50 minutes at 350°F (180°C), fan setting. If the top darkens too quickly, shield it with a sheet of parchment.
Give the cake a few minutes out of the oven. Then melt the apricot jam (½ cup/175 g) over low heat and glaze the surface and edges. Wait until it reaches room temperature to cut and serve. Enjoy!