In a large mixing bowl, whisk together flour, baking powder, and a pinch of salt and pepper until well combined and lump-free.

Add softened butter to the dry ingredients and mix until resembling coarse crumbs.

Crack in the egg and mix until a uniform dough forms.

Fold in diced ham and grated cheese, and optional mustard, ensuring even distribution.

Preheat the oven to 180°C (355°F) while preparing a baking tray lined with parchment paper.

Scoop out small balls of dough, place on the tray, and flatten slightly.

Bake in the preheated oven for 12 to 15 minutes, until golden around the edges.

Let the cookies cool on a wire rack for about 5 minutes before serving.