Preheat the oven to 180°C (160°C fan/ 350°F).
Pour 2 tbsp of the melted butter into a bundt tin - I used a 12-cup bundt tin but you can use a 6-cup bundt tin if you have one. Use a pastry brush to coat the whole inside of the tin with the butter, getting into all the crevices. Add a little bit of the flour then tap & tilt the pan around to coat the bundt tin as well as possible, tapping out excess flour into a large bowl.
Pour the remaining melted butter into that large bowl along with the sugar and eggs. Beat together until smooth. Add the orange zest, poppy seeds, salt and buttermilk. Mix until smooth.
Add the flour, ground almonds and baking powder, then fold in gently until just mixed. Pour into the prepared bundt tin.
Bake for 25-35 minutes (baking time will depend on the bundt tin used), until a toothpick inserted into the centre comes out clean.
Remove from the oven, let cool in the tin for 10 minutes before tipping out onto a wire rack to cool completely.
Mix the glaze ingredients together in a small bowl, adding enough juice to get a thick but pourable glaze. Pour it over the cooled cake. Decorate with flaked almonds/dried flowers if desired.