To make the brown butter, melt butter in a clear heavy bottom pot. Once the butter starts to foam, whisk continuously until brown bits start to form. Remove from heat, pour into clean bowl, skim the foam from the top and cool to room temperature (30 minutes).
Combine all ingredients for the streusel topping in a bowl. Mix until well combined and large crumbles form. Place in the fridge until ready to top the pumpkin bread. When ready to top, take large crumbles and break down into smaller crumbles on top of the pumpkin batter.
Line 9×5 loaf pan with parchment paper, leaving 1-2 in. overhang on the sides. Preheat oven to 350F. Whisk together flour, baking powder, baking soda, salt and pumpkin spice. Set aside.
In a stand mixer with paddle attachment (or by hand), cream browned butter, and sugar until smooth and well combined. Add eggs, beating well after each one until well combined. Add pumpkin puree and vanilla bean paste, beating until well combined.
In this order (dry ingredients, yogurt, dry, yogurt, dry), add dry ingredients to the wet alternating with the yogurt. Slowly beat each time until JUST combined. A few flour streaks is okay! Gently pour into prepared pan. Top with walnut streusel.
Bake at 350F for 45 minutes. Check the topping. If its browning too quickly, top with a foil tent. Return to the oven for 10-15 minutes, checking for doneness every 5 minutes (55-65 minutes total). When a toothpick inserted into the center comes out clean or with a few moist crumbs, its done. Cool in pan for at least 30 minutes. If topping with glaze, you can pour the glaze directly on top while the bread is in the pan. For a drip effect, remove pumpkin bread from the pan (after 15-20 minutes), place back on cooling rack and pour glaze directly onto the bread. Allow 30 minutes for the glaze to softly set or an hour for a firm set.