Pre-heat oven to 170°C/160°C (fan oven)/gas mark 4 and line and grease a 9x13” rectangular cake tin.
First make the crumble topping by rubbing together all the ingredients except the cheddar. Then stir in the cheddar cheese. Spread out onto a baking sheet and place in the freezer whilst you prepare the rest of the cake.
In a large bowl sift the flours together with the baking powder, bicarbonate of soda, salt, thyme leaves and set aside.
Cream the butter and sugar in a food mixer for 10 minutes until light and fluffy.
Add the eggs, beating in one by one then add the vanilla extract.
Spoon in 1/3 of the flour mix, beat into the batter then add 1/2 of the sour cream and beat in. Repeat again and then add the last 1/3 of flour mix, beating until the batter is smooth.
Pour half of the cake mixture into the cake tin, then tumble in half of the chopped apples. Pour the rest of the cake mixture over, smooth and then scatter the rest of the apples over the top.
Finally sprinkle over the crumble topping so all the apples are covered.
Bake in the oven for 50 minutes, check after 25 minutes and if you think the cheese is browning too much then place a loose sheet of tin foil over the top of the cake tin for the rest of the bake.
Remove the cake from the oven, leave to rest for 5 minutes then carefully remove from the tin.
Let the cake cool completely on a wire rack until you decorate with the glaze.
To make the glaze mixing the icing sugar with the milk until thick but pourable. Drizzle over the cake and then leave to set for at least an hour before cutting into squares.