Maple Sour Cream Walnut Muffins

I saw this recipe on design*sponge and it looks absolutely delicious!

(makes approximately 12 standard sized muffins)

For the batter:

1/2 cup butter, room temperature
3/4 cup maple syrup
2 large eggs
1 cup sour cream
1 tsp vanilla extract
2 cups all purpose flour
1 tsp baking soda
2 tsp baking powder
1/2 tsp salt
1/2 tsp cinnamon
1/4 cup walnuts, roughly chopped

For the topping:

1/2 cup brown sugar
1/2 cup all purpose flour
3 Tbs butter, chopped
Scant 1/4 cup walnuts, chopped small
1/2 tsp cinnamon

Whip butter in an electric mixer. Slowly add maple syrup to combine. Add eggs, one at a time. Add sour cream. Add vanilla extract. Combine dry ingredients (except nuts). Add to butter mixture. Stir to combine. Stir in walnuts. Fill muffin cups approximately half full with batter.

Combine ingredients for the topping. Use your fingers to pinch butter and break into pea-sized pieces well-combined into rest of ingredients. Generously spoon topping over muffin batter.

Bake in 350 degree oven for 10-12 minutes until a cake tester comes out clean. Cool on wire racks.