In a large bowl, sift all-purpose flour, baking powder, baking soda, cinnamon, nutmeg and salt. Set aside.

In another bowl, add eggs, sugar, vanilla and lemon zest and mix until combined and thick.

Melt the butter and slowly add to the egg/sugar mixture.

Add the sour cream and mix until combined.

Make a well in the center of the dry ingredients and pour the wet ingredients in the center of the well.

Use a spatula to fold the wet ingredients into the dry ingredients until just combined.

Wrap the dough in plastic wrap and refrigerate for at least an hour or overnight.

To cook the donuts, fill a large pot with vegetable oil (at least 2" high) and clip a candy thermometer to it.

Make the glaze by heating butter over medium heat in a sauce pan until melted. Continue to brown butter until fragrant and a golden brown. Transfer to a heat proof mixing bowl.

Add powdered sugar, vanilla, maple syrup and 2 tablespoons milk to the butter and mix until smooth.

Heat the oil in the large pot to 350 degrees.

While the oil is heating, turn your dough out onto a lightly floured surface.

Sprinkle flour on top of dough and roll out the dough to 1/2" thickness.

Use a donut cutter or cookie cutters to cut out donuts from dough.

When your oil is 350 degrees, carefully lower 2-3 donuts into the oil.

Fry the donuts for a minute or 2 on each side or until golden brown.

Use a slotted spoon to place donut on a paper-towel lined plate to drain for a couple of minutes.

Dip each donut into the glaze and place on a wire rack to cool and dry.